A =
Upon observing the given code, I have understood that you are trying to substitute the differential expressions in the matrix with shorter & new symbols.
I have found a workaround for the task which you are trying to accomplish, in the MATLAB documentation I have found a function named “str2sym” which converts the string version of a symbolic expression to original symbolic expression type.
Using this function, the expressions which are to be replaced can be given as input to the “subs” function as a cell array of symbolic types as shown here:
syms theta(t) t psi(t)
A=[diff(theta(t),t) -diff(psi(t),t); -diff(theta(t),t) diff(psi(t),t)] % Initial given matrix where substitution has to be done.
theta2 = str2sym('theta2(t)')
psi2 = str2sym('psi2(t)')
subs(A,{str2sym("diff(theta(t),t)"),str2sym("diff(psi(t),t)")},{theta2,psi2})% Using str2sym function to convert strings to symbolic expressions and pass them into subs as argument.
by using this the required substitutions can be performed correctly as required.
Here is the link for the MATLAB documentation stating the usage of “str2sym” and “subs” functions :
- https://www.mathworks.com/help/symbolic/str2sym.html
- https://www.mathworks.com/help/symbolic/sym.subs.html
I hope this helps in achieving the desired output.
