matric component of symbolic fuction

I'm using matlab live editor and trying to get a specific component of a variable function of matric

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clc

clear all

syms r Phi(r) Lambda(r) theta t phi

xa=[t;r;theta;phi]

n=4;

g=[-exp(-2*Phi),0,0,0; 0, exp(-2*Lambda),0, 0; 0,0,r^2*theta^2,0; 0,0,0,r^2* (sin(theta))^2 ]

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for example I would like to have g(1,1) but g is function of r, g(1,1) doesn't work...

Is there any good way to figure our this problem..?

I need "for" loop to calculate some symbolic algebra for each component

Thanks in advance

Answer 1

[Walter Roberson]

There is no way to do that in MATLAB, at least not without knowing the internal operations of the Symbolic engine.

In MATLAB when you create a symbolic function that is non-scalar, there is no way (short of internal operations) to index the function to get to one particular calculation.

You have several options at this point:

• call the symbolic function passing in symbolic parameters, getting out a symbolic array that you then index; or
• create g as a cell array instead of using []. You would not be able to directly do things such int(g) or directly evaluate g at a parameter, but you would be able to index; or
• use unsupported calls into the symbolic engine and arcane knowledge to do the indexing.