MATLAB: Fsolve with another function

Question

Hey,

I have a function which looks like:

function F = ex5(A_CL)
% Constants
theta = 86/180*pi; 
delta_GL = 3.28*10^-10; %[m]
gamma_L = 0.0728; %[J/m^2]
N = Inf;
% equation to solve
F = gamma_L*(1+cos(theta))-vdW_layer(delta_GL, A_CL,N);
end

This function calls up another funcition vdW-layer(delta_GL, A_CL, N).

Now I want to solve the function/ find out the A_CL, having delta_GL and N as input variables and A_CL remains unknown.

I tried with this code:

fun5 = @(A_CL) ex5(A_CL);
A_CL_init = 10e-78; %initial guess
[A_CL, fval] = fsolve(fun5, A_CL_init);

where is my mistake??

thanks a lot!!!

Answer 1

You have to edit your ‘ex5’ function to allow it to use extra input arguments:

function F = ex5(A_CL, delta_GL, N)
% Constants
theta = 86/180*pi; 
% % delta_GL = 3.28*10^-10; %[m]                   % Now An Input Argument, So Delete Here
gamma_L = 0.0728; %[J/m^2]
% % N = Inf;                                       % Now An Input Argument, So Delete Here
% equation to solve
F = gamma_L*(1+cos(theta))-vdW_layer(delta_GL, A_CL,N);
end

Then this changes to accommodate the new inputs to ‘ex5’:

delta_GL =  . . .;
N = . . .;
fun5 = @(A_CL) ex5(A_CL, delta_GL, N);
A_CL_init = 10e-78; %initial guess
[A_CL, fval] = fsolve(fun5, A_CL_init);

Note: I did not run your code, so I’m labeling my changes as UNTESTED CODE, however it should work.