How to set an assumption on a symbolic variable in a symbolic expression?

Question

xv cheng 2018-8-6

评论： Walter Roberson 2018-8-6

Hello!

I want to solve some equations using symbolic math toolbox.I only get some strings like '3*x1-2*x2'.x1,x2 should be positive numbers.

I can use str2sym(string) to get a symbolic expression 3*x1-2*x2.

Then, how to set an assumption on x1,x2 in the symbolic expression? The assumption is x1>0,x2>0.

Thank you in advance

Answer 1

Stephan 2018-8-6

编辑：Stephan 2018-8-6

Hi,

you can use the assume function for this purpose.

Note the section for multiple assumptions which requires assumeAlso to work properly.

Best regards

Stephan

Walter Roberson 2018-8-6

You can symvar to get the variable names and arrayfun assume()