Any form of simplify method, or at least expanding the expressions, available?

[Panagiotis Stavropoulos]

Hello,

I am using this package to do symbolic calculations with c++.

First of thank you to the developers for this very useful package!

Now my actual issue. I am using SymEngine::Expression to store symbolic expressions and in the actual calculation their are a lot of operations of the form x*y+z*w, where x,y,z,w are expressions. I am running into an issue where basic simplifications are not happening. Following is a very simple program showing this behaviour:

Program in file test_basic_prob.cpp:

#include <symengine/cwrapper.h>

#include <symengine/expression.h>

int main(){

// Declerations

SymEngine::Expression b("b");

SymEngine::Expression a("a");

SymEngine::Expression x, y, w, z;

SymEngine::Expression res;

// Set up expressions

x = SymEngine::Expression(-3);

y = (SymEngine::Expression(3)-a);

z = (-SymEngine::Expression(9)+b);

w = SymEngine::Expression(-1);

res = x*y + z*w;

// Print results;

std::cout << " x = " << x << std::endl;

std::cout << " y = " << y << std::endl;

std::cout << " z = " << z << std::endl;

std::cout << " w = " << w << std::endl;

std::cout << " x*y + z*w = " << res << std::endl;

return 0;

}

Compile and output:

icpc -std=c++14 -c -I/usr/local/include/symengine test_basic_prob.cpp -o test_basic_prob.o

icpc -std=c++14 -I/usr/local/include/symengine -o test.out test_basic_prob.o -L/usr/local/lib -lsymengine -lgmp

./test.out

  x = -3

  y = 3 - a

 z = -9 + b

 w = -1

 x*y + z*w = -(-9 + b) - 3*(3 - a)

As you can see their is no problem compiling and running. The final result in res variable should have clearly been a - b or -b + a. However nothing is simplifying.

This issue is worst when a and b are the same variable, and the expression will not simplify to zero.

I tried going through the test programs to see if their is any instruction in the package to do this but I cannot seam to figure it out. Is their a way around this issue?

[Isuru Fernando]

You can use expand as in https://github.com/symengine/symengine/blob/master/symengine/tests/expression/test_expression.cpp#L58.

In SymEngine, distribution of multiplication is not considered simple and is not done automatically. To do this you have to explicitly call expand.

Isuru

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[Panagiotis Stavropoulos]

Ok works great. That was simple! Thank you.