Conversion to double from function_handle is not possible.

Cold someone help me with this. I'm trying to solve multiple ode s simultaneously. It says "Conversion to double from function_handle is not possible."

Here's the code

clc
clear all

[t,xa] = ode15s(@f,[0 80*3600],zeros(2499,1));    

function dydt3 = f(t,x)
cpo=1e-7;
d=1.3;
p=5.7e-3;
dx=65/100;

dcdt=zeros(50,50);
for i=2:49
    for j=2:49
         dcdt(i,j)= @(x) (d*((x(i+1,j)+x(i-1,j)+x(i,j+1)+x(i,j-1)-4*x(i,j))/(dx^2)))
    end
end
for j=2:49
    dcdt(1,j)= @(x) (d*((x(1+1,j)+x(1+1,j)+x(1,j+1)+x(1,j-1)-4*x(1,j))/(dx^2)))
end

for i=2:49
    dcdt(i,1)= @(x) (d*((x(i,1+1)+x(i,1+1)+x(i+1,1)+x(i-1,1)-4*x(i,i))/(dx^2)))
end

for j=2:49
    dcdt(50,j)= @(x) (d*((x(50-1,j)+x(50-1,j)+x(50,j+1)+x(50,j-1)-4*x(50,j))/(dx^2)))
end

for i=2:49
    dcdt(i,50)= @(x) (d*((x(i,50-1)+x(i,50-1)+x(i+1,50)+x(i-1,50)-4*x(i,50))/(dx^2)))
end

dcdt(50,1)=@(x) (d*((x(49,1)+x(49,1)+x(50,2)+x(50,2)- 4*x(50,1))/(dx^2)));
dcdt(50,50)=@(x) (d*((x(49,50)+x(49,50)+x(50,49)+x(50,49)-4*x(50,50))/(dx^2)));
dcdt(1,50)=@(x) (d*((x(1,49)+x(1,49)+x(2,50)+x(2,50)-4*x(1,50))/(dx^2)));
x(1,1)=@(x,t) ((d*x(1,2)+(dx*p*(cpo*((ap*exp(la.*t))+(1-ap)*exp(lb.*t)))))/(p*dx+d));
dcdt2= @(x,t) reshape(dcdt,[2500,1])
for i=1:2499
    dcdt3(i)= dcdt2(i+1)
end
%dydt3 = dydt3';

end

Answer 1

[James Tursa]

You can't store function handles inside a double variable. You must use a cell array instead. E.g.,

>> f = zeros(2,1);
>> f(1) = @(x)x^2
??? The following error occurred converting from function_handle to double:
Error using ==> double
Conversion to double from function_handle is not possible.

>> f = cell(2,1);
>> f{1} = @(x)x^2
f = 
    @(x)x^2
    []
>> f{2} = @(x)x^3
f = 
    @(x)x^2
    @(x)x^3
>> f{1}(4)
ans =
    16
>> f{2}(4)
ans =
    64

That being said, it is not clear to me why you are trying to create an array of function handles.

[Lakshay Sethi]

Thanks again but I'm new to matlab and not very familiar with the jargon. Could you please elaborate your answer or tell me what's wrong with my code.

[Walter Roberson]

Remove all of the @(x) and @(x,t). For example, rather than

dcdt(i,j)= @(x) (d*((x(i+1,j)+x(i-1,j)+x(i,j+1)+x(i,j-1)-4*x(i,j))/(dx^2)))

use

dcdt(i,j)= (d*((x(i+1,j)+x(i-1,j)+x(i,j+1)+x(i,j-1)-4*x(i,j))/(dx^2)));