Interview Questions.

Question 1. What Is Scip?

Answer :

SCIP is a solver for Mixed Integer Linear and Nonlinear Problems that allows for an smooth integration of arbitrary constraints. It may be used as a framework for branch-cut-and-charge and contains all essential plugins to function a standalone solver for MIP and MINLP.

You can use the precompiled binaries to clear up MIPs and MINLPs. Learn extra approximately the document formats supported through SCIP, and get an outline of the supported problem training and extra pointers for solving them.
You can use SCIP as a subroutine for fixing MINLPs and more trendy constraint integer packages from your very own supply code.
You can use SCIP as a framework in that you enforce your own plugins.
You can use SCIP in any mixture of the three purposes above.
Question 2. When Should I Use Scip?

Answer :

If you are either looking for a quick non-business MIP/MILP-solver or for a department-reduce-and-price-framework wherein you can at once put into effect your very own techniques and lets in full control of the solving process.

SSIS(SQL Server Integration Services) Interview Questions
Question three. How Do I Get Started?

Answer :

An easy manner is to use the SCIP-binaries and call SCIP from a shell, see right here for a tutorial. For that, you just should down load one of the precompiled binaries from the down load phase, or the zipped supply code and assemble it along with your favorite settings. This is described in detail inside the INSTALL report inside the SCIP main directory.

Another manner is to apply SCIP as a solver included into your personal program supply code. See the directories "examples/MIPsolver/" and "examples/Queens/" for simple examples and this point.

A 0.33 manner is to put into effect your very own plugins into SCIP. This is defined within the How-to be for all plugin sorts, which you could locate within the doxygen documentation.

Question 4. Do I Need Any Extra Software?

Answer :

Unless you want to use SCIP as a natural CP-Solver (see here), you want an underlying LP-Solver established and linked to the libraries (see the INSTALL report inside the SCIP root listing).

LP-solvers presently supported by using SCIP are:

SoPlex
IBM ILOG CPLEX
FICO XPress
Gurobi (model at least 7.Zero.2 required)
CLP (interface currently every so often produces incorrect outcomes)
Glop, Google OR equipment (experimental, LPI contained in OR gear)
Mosek
QSopt (experimental)
We additionally offer a few precompiled binaries. Besides that, you may want a modeling language like ZIMPL to generate *.Mps or *.Lp documents. ZIMPL files can also immediately be read by SCIP. You can down load a package which incorporates SCIP, SoPlex and ZIMPL here.

If you want to use SCIP for mixed integer nonlinear programming, you might want to apply an underlying NLP solver (e.G., Ipopt). SCIP already comes with the CppAD expression interpreter (e.G., CppAD) as part of the supply code.

Question five. How Can I Debug In Scip?

Answer :

Compile SCIP in debug mode: make OPT=dbg. Put the binary into a debugger, e.G., gdb and permit it run again. If you get an affect which factor is causing the hassle, set #define SCIP_DEBUG because the first line of the corresponding *.C record, recompile and let it run again. This will print debug messages from that piece of code.

Advanced C++ Interview Questions
Question 6. Can I Use Scip As A Pure Cp/sat Solver?

Answer :

Yes. SCIP can be used as a pure CP/SAT Solver by using typing set emphasis cpsolver within the shell or by the usage of the feature SCIPsetEmphasis (). Furthermore, you may compile SCIP without any LP-Solver by using make LPS=none.

Question 7. Can I Use Scip As A Pure Lp-solver?

Answer :

Since LPs are most effective special kinds of MIPs and CIPs, the primary answer is sure. If you feed a natural LP to SCIP, it will first observe presolving after which hand this presolved problem to the underlying LP solver. If the LP is solved to optimality, you can question the most desirable solution values as continually. You also can get admission to the values of an ideal dual solution through the usage of show twin solution.

However, there are positive limitations to this: Reduced costs are not accessible. If the LP seems to be infeasible, you can not currently achieve a Farkas evidence. And take into account that this approach is most effective meaningful if the trouble is an LP (no integer variables, handiest linear constraints).

Hence, in case you need greater, "LP particular", facts than the primal answer, you're higher off using an LP-Solver at once. If you're the usage of the SCIP Optimization Suite, you can, e.G., use the covered LP solver SoPlex. If you want to solve an LP no longer from the command line, but within your C/C++ application, you may also use SCIP's LP-Interface.

C and C++ Interview Questions
Question 8. Which Kind Of Minlps Is Supported By Scip?

Answer :

SCIP supports nonlinear constraints of the shape lhs ≤ f(x) ≤ rhs, in which the feature f(x) is an algebraic expression that can be represented as expression tree. Such an expression tree has constants and variables as terminal nodes and operands as non-terminal nodes. Expression operands supported with the aid of SCIP include addition, subtraction, multiplication, department, exponentiation and logarithm. Trigonometric capabilities aren't yet supported by SCIP.

Nonlinear objective capabilities are not supported through SCIP and need to be modeled as constraint characteristic. Note, that the assist for non-quadratic nonlinear constraints is not yet as strong as the rest of SCIP. Missing bounds on nonlinear variables and tiny or massive coefficients can without problems result in numerical issues, which may be prevented by way of cautious modeling.

Question 9. How Can I Build/bring together Scip?

Answer :

SCIP may be compiled the use of both Make documents or CMake. It's endorsed to use the new CMake construct system both for brand spanking new and long-time users of SCIP. Consult the CMake documentation for further statistics about the changes delivered within the new device (like Linux-conform naming conventions for libraries). We nevertheless guide the conventional Make file machine for backwards compatibility however it is probably discontinued in some unspecified time in the future.

Question 10. What Is This Business With .A And .So Libraries In The Directory Lib?

Answer :

When SCIP builds the binary, it desires to hyperlink with the corresponding libraries, i.E., its own libraries and people of an LP-solver. There are normally  approaches to distribute a library (on UNIX structures). In the first (with suffix ".A"), the library is related statically to SCIP; which means that all records is packed into the binary. In the second one manner (with suffix ".So"), the library is a shared library. In this situation, the code of the library isn't inserted into the binary itself, but is loaded at runtime. This has the gain that the binaries are smaller, however it comes on the cost that you need to make sure that the library is observed at runtime. (SCIP adds rpath records containing the route to the shared libraries to the binary; this commonly permits finding these libraries at runtime. If this does not work, for most structures it suffices to position the course of the library into the LD_LIBRARY_PATH surroundings variable).

There are compiler-based alternatives which version ought to be included if both a static and a shared model of the identical library are available. In order to keep away from confusion, SCIP separates shared from static libraries into the directories "lib/static" and "lib/shared" when using the Makefile machine. Note that a few LP-solvers are best shipped with a shared model.

Question 11. Can I Compile Scip As A Shared Library?

Answer :

You can use the SHARED=actual alternative whilst making SCIP. This will generate the libraries of SCIP in shared layout. The binary then additionally makes use of this shape. Note that the route to the lib/shared listing of SCIP is used to find the libraries. If you need to transport the libraries, you would possibly want to set the LD_LIBRARY_PATH surroundings variable to encompass the new direction. If you are using your very own build gadget: The "magic" changes are the -fPIC compiler/linker option and the -Wl,-rpath alternative.

Question 12. The Methods Scipgetvarsol () And Scipvargetsol () Seem To Have The Same Functionality. Which One Should I Use?

Answer :

In truth, there may be a mild difference: SCIPvarGetSol () is likewise able to return pseudo solution values. If you do not have an idea, what pseudo solutions are, SCIPgetVarSol () ought to be simply quality. This have to be the most effective case of 'duplicate methods'.

SSIS(SQL Server Integration Services) Interview Questions
Question 13. Is There A Way To Visualize The Branch And Bound Tree?

Answer :

Here is a list of outside tools that can be used to create interactive and no interactive visualizations in diverse codecs.

HyDraw can show a stay visualization of the tree the usage of Java View.
Vbctool comes with a viewer that has an choice to uncover the nodes one-through-one (every time you hit the space key). Additional node statistics along with its decrease bound, intensity, and variety are accessed via a context menu.
Vbc2dot is a script that generates a visualization of SCIP's department-and-certain tree in ps and pdf layout. It is written in Ruby and calls for dot (graphviz).
ZimplTblConverter is a small Ruby-script that converts a scip solution report to a file wherein all names are changed in line with a zimpl tbl-report output.
Grumpy is a Python device that permits creating no interactive visualizations of the tree in numerous formats.
For using this kind of equipment, SCIP helps you to define file names set visible vbcfilename somefilename.Vbc and set visual bakfilename somefilename.Dat. Grumpy uses BAK files while the opposite tools parse vbc output.

For folks who need to use the step-by means of-step capability of vbctool, it is important to use a time-step counter for the visualization instead of the actual time. The corresponding parameter is modified via set visible realtime FALSE.

For users of the callable library, the corresponding parameters are known as "visible/bakfilename", "visible/vbcfilename", and "visible/realtime".

Question 14. Scip Has Found Decent Primal And Dual Bounds But Still Reports The Gap As "infinity". Why?

Answer :

By default, the SCIP output includes the show column "hole", that's computed as follows: If primal and dual bound have contrary signs, the distance is "Infinity". If primal and dual sure have the equal signal, the spaceprimal certain - dual suredualboundadvantage that the distance decreases monotonously for the duration of the solving process.

An alternative definition of the distance is (twin certain - primal bound) / abs (primal bound). Using this definition, a finite hole is computed as soon as a dual and primal bound had been found. However, the space may additionally growth at some stage in the fixing technique, if each bounds have opposite symptoms in the beginning. In SCIP, this definition can be blanketed within the output with the aid of allowing the display column "primal gap": display/primal gap/energetic = 2

Question 15. Scip Crashes During Symmetry Detection With Bliss. What Can I Do?

Answer :

The bliss library can be compiled with or without GMP help. If bliss is compiled with GMP the macro definition BLISS_USE_GMP should be introduced, in any other case the headers do not suit the library which produces the crash. If bliss is compiled as shared library, the CMake system must be capable of hit upon this robotically.

In case you do not want symmetry coping with, the very best manner to solve the problem is to simply disable symmetry handling throughout compilation (see Make files or CMake) or with the SCIP parameter misc/use symmetry = zero. Otherwise it could be resolved by means of both including the macro definition with the compiler flag -DBLISS_USE_GMP or via compiling bliss otherwise, i.E. With out GMP help.

Question sixteen. The Output Is Too Wide For My Terminal Window. What Can I Do?

Answer :

In the interactive shell you can set the width of the output with the subsequent command set display width observed via the suitable quantity.

Question 17. What Do The Cryptic Abbreviations For The Columns Mean Which Are Displayed During The Solving Process Of Scip?

Answer :

Type display inside the interactive shell to get an evidence of them.
By the way: If a letter appears in front of a show row, it suggests, which heuristic determined the brand new primal sure, a star representing an imperative LP-rest.
Typing display facts after completing or interrupting the fixing technique offers you plenty of greater information approximately the fixing procedure (Typing show heuristics offers you a listing of the heuristics including their letters.)
Question 18. Why Does Scip Claim That It Could Not Find The User Parameters "scip. Set"? Where Can I Get Such A File?

Answer :

SCIP comes with default settings which might be automatically active when you begin the interactive shell. However, you have the possibility to save customized settings thru the set save and set diffusive instructions. Both instructions will set off you to enter a file call and keep both all or custom designed parameters best to the desired report.

A person parameter file that you save as "scip. Set" has a unique that means; each time you invoke SCIP from a listing containing a document named "scip. Set", the settings therein overwrite the default settings. For more statistics about custom designed settings, see the Tutorial at the interactive shell. Settings documents can come to be incompatible with later releases if we determine to rename/delete a parameter. Information about this could be determined inside the CHANGELOG for each launch.

Advanced C++ Interview Questions
Question 19. How Do I Change The Behavior Of Scip?

Answer :

You can switch the settings for all pre fixing, heuristics, and separation plugins to a few extraordinary modes thru the set pre solving, heuristics, separation emphasis parameters inside the interactive shell. Off turns off the respective type of plugins, fast chooses settings that cause much less time spent on this sort of plugins, lowering their effect, and competitive increases the impact of this sort of plugins. You can integrate those general settings for cuts, pre fixing, and heuristics arbitrarily.

Display parameters shows you which ones settings currently range from their default, set default resets them all. Furthermore, there are whole settings that can be set by set emphasis, i.E. Settings for pure feasibility troubles, solution counting, and CP like seek.

Question 20. How Can I Input A Minlp Into Scip?

Answer :

Please consult this assessment at the hassle classes supported by SCIP and the tips and links for MINLPs therein.

Question 21. How Do I Construct A Problem Instance In Scip?

Answer :

For starters, SCIP comes with whole examples in source code that illustrate the trouble introduction system. Please talk over with the examples of the Callable Library section in the Example Documentation of SCIP.
First you have to create a SCIP item through SCIPcreate (), you then start to construct the trouble via SCIPcreate Prob (). Then you create variables thru SCIPcreate Var () and add them to the trouble thru SCIPaddVar ().
The same needs to be executed for the limitations. For instance, if you need to fill inside the rows of a general MIP, you have got to call SCIPcreateConsLinear (), SCIPaddConsLinear () and moreover SCIPreleaseCons () after completing. If all variables and constraints are present, you can initiate the answer manner through SCIPsolve ().
Make sure to additionally name SCIPreleaseVar () in case you do no longer want the variable pointer anymore. For an evidence of making and releasing objects, please see the notes on releasing items.
Question 22. What Operational Stages Of Scip Are There And Are They Important For Me?

Answer :

There are fourteen unique stages all through a run of SCIP. There are a few methods which cannot be referred to as in all tiers, don't forget

For Example: SCIP trySol ().

Question 23. What Is The Difference Between The Original And The Transformed Problem?

Answer :

Before the solving system begins, the authentic trouble is copied. This copy is called "transformed hassle", and all adjustments all through the pre solving and solving system are handiest applied to the converted hassle.

This has two essential blessings: first, the user also can alter the problem after in part solving it. All adjustments completed via SCIP (pre solving, cuts, and variable fixings) during the partial fixing method will be deleted together with the converted hassle; the consumer can alter the authentic trouble and restart solving. Second, the feasibility of answers is constantly tested at the original hassle!

Question 24. What Is Scip_call ()? Do I Need This?

Answer :

Yes, you do. SCIP_CALL () is a worldwide outline, which handles the go back codes of all methods which go back a SCIP_RETCODE and must therefore parenthesize each such technique. SCIP_OKAY is the code which is again if the whole thing worked well; there are 17 specific mistakes codes, see type_retcode.H.

Each approach that calls techniques which return a SCIP_RETCODE must itself go back a SCIP_RETCODE. If this isn't always feasible, use SCIP_CALL_ABORT () to trap the return codes of the strategies. If you do not want to apply this both, you need to do the exception dealing with (i.E. The case that the return code is not SCIP_OKAY) to your personal.

C and C++ Interview Questions
Question 25. Is It Possible To Avoid That The Scip Library Overrides My Signal Handler For Interruptions?

Answer :

By default, the SCIP library has an inner handler for the handling of the SIGINT signal, that's normally emitted whilst a consumer presses CTRL-C during the answer system. In cases where this overrides the sign coping with of a surrounding utility, this will be undesirable. As a remedy, the parameter misc/catchctrlc may be set to FALSE or the SCIP library can be compiled with the unique C compiler flag "-FNO SIGACTION", each disabling SCIP's internal sign handling.

Question 26. Can I Remove Unnecessary Display Columns Or—even Better—upload My Own Ones? Can I Change The Statistics Displayed At The End Of Solving?

Answer :

Setting the fame of a display column to zero turns it off. E.G., type set display memused popularity 0 within the interactive shell to disable the memory facts column, or include the road SCIP setIntParam (scip, "display/memused/repute", 0) into your source code. Adding your personal show column can be completed by means of calling the SCIP includeDisp () approach, see the doxygen documentation.

The statistic show, which is shown by show facts and SCIP print Statistics (), respectively, can't be modified.

Question 27. What Do Lp-rows Look Like In Scip?

Answer :

Each row is of the shape lhs ≤ Σ(val[j]•col[j]) + const ≤ rhs. For now, val[j]•col[j] may be interpreted as aij•xj (for the difference between columns and variables see here). The regular is basically wished for amassing the influence of presolving reductions like variable fixings and aggregations.

The lhs and rhs may additionally take endless values: A less-than inequality might have lhs = -∞, and a greater-than inequality could have rhs = +∞. For equations lhs is equal to rhs. An limitless left hand facet may be recognized by means of SCIPisInfinity (scip, -lhs), an countless proper hand side can be identified by means of SCIPisInfinity (scip, rhs).

Question 28. What Is The Difference Between Columns And Variables, Rows And Constraints?

Answer :

The terms columns and rows usually talk to the representation in the cutting-edge LP-rest, variables and constraints on your global Constraint Integer Program.

Each column has an related variable, which it represents, but now not each variable have to be part of the contemporary LP-rest. E.G., it could be already constant, combination to every other variable, or be priced out if a column generation approach became carried out.

Each row has either been introduced to the LP via a constraint handler or with the aid of a reducing aircraft separator. A constraint handler is able to, but does not need to; upload one or more rows to the LP as a linear rest of each of its constraints. E.G., inside the typical case (i.E. With out using dynamic rows) the linear constraint handler provides one row to the LP for each linear constraint.

Question 29. Are The Variables And Rows Sorted In Any Particular Order?

Answer :

The variable array which you get via SCIPgetVarSol () is internally looked after by way of variable kinds. The ordering is binary, integer, implicit integer and continuous variables, i.E., the binary variables are saved at function [0... Nbinvars-1], the general integers at [nbinvars... Nbinvars+nintvars-1], and so on. It holds that nvars = nbinvars + ninitvars + nimplvars + ncontvars. There is no in addition sorting within those sections, in addition to there's no sorting for the rows. But each column and every row has a completely unique index, which may be received by means of SCIPcolGetIndex () and SCIPcolGetIndex (), respectively.