MATLAB: Fsolve problem with syms var

fsolve symsMATLAB

dear all

i write cod that i want to solve it with fsolve commend

at the end, my equations just contain double parameters but in the middle of my function i must consider some symbolic parameters that i remove them after some calculations

but when i run my function i got error : FSOLVE requires all values returned by functions to be of data type double and point the line i define my symbolic variable but i mention again that my final equation doesnt contain any of those symbolic var

is there any way to my problem

Best Answer

It is not possible to do what you are asking to do.

I already told you what you need to do to solve this: you need to run your code symbolically, and then use matlabFunction to convert the resulting symbolic expressions to function handles.

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MATLAB: Call large equation to ode solver

function dy = shebhestatici1(t,y)
    X1=y(1,1);
    X2=y(2,1);
    X3=y(3,1);
    X4=y(4,1);
    X5=y(5,1);
    X6=y(6,1);
    M = function_where_you_supply_M(X1,X2,X3,X4,X5,X6);
    G = function_where_you_supply_G(X1,X2,X3,X4,X5,X6);
    xdd=-M\G;
    dy=xdd;
end

MATLAB: FSOLVE requires all values returned by functions to be of data type double.

If you want to solve a system of equations symbolically or using symbolic variables, use the solve function instead of fsolve. The fsolve function requires that the output of the function you specify as the first input be double precision numbers, not symbolic expressions.

If you must use fsolve with symbolic variables inside the function, you must convert those symbolic expressions into numbers using double before returning the numbers (not the symbolic expressions) from the function.

As a very simple example, put all this code into a function example373677.m and run it:

function y = example373677
y = fsolve(@mysubfun, 3);
 
function z = mysubfun(q)
x = sym('x');
r = x.^3-2*x-5;
z = double(subs(r, q));

Of course, with solve this is easier.

syms x
y = solve(x.^3-2*x-5)

You may need to use vpa to approximate y numerically.

vpa(y)

One of the solutions returned in y should match the result you received from running the function.

Best Answer

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MATLAB: Call large equation to ode solver

MATLAB: FSOLVE requires all values returned by functions to be of data type double.

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