rewriting symbolic equations (e.g. f(x1, x2, x3)) as f(x1, y=x2+x3)after calculating the function limit when x2-->inf

Hi, is there a way to do the following in Matlab: 1) I have 2 complicated equations V=f(x1,x2,x3) and D=f(x1,x2,x3)

I wanna create a third function G such that G=4D *(3V+D)/3V+4D

but I want G to be G=f(x1,z) where z is related to x2 only (in my problem, x3-->inf and I have an expression to relate z to x2).

also, 2) is there a way to get a simplified expression of a symbolic equation (i.e. written in terms of undefined variables) when one of its variables goes to inf

thanks for any help on the above.

Answer 1

[mslim]

Thanks Walter for pointing out those functions. are you sure that evalAt is an option? the matlab functions are not doing a good job simplifying the expression. also, I am not getting an acceptable answer obtaining the limits of the expression (setting one parameter-->inf) simplified by matlab.

thanks rgds

Answer 2

[Walter Roberson]

See evalAt and simplify

You will be able to call simplify() directly from the MATLAB level, but evalAt will need to be called within the symbolic engine, such as using feval(symengine, 'evalAt', G, [x3=inf])

[Sean de Wolski]

Welcome back Walter!