Unrecognized function or variable in a code

% param value
clear all; close all;
% p is constant and q varies
k0 = 0.0000169; u=0.6; p=536.2; q=0.0000376;
% your function
 k = @(t,u) (k0 + (p*k0.^u-q*k0).*t.^a/gamma(a+1) +(p*k0.^u-q*k0).*(p*u*k0.^u-q).*t.^(2*a)/gamma(2*a+1)...
  +(p*k0.^u-q*k0).*((p*u*k0.^u-q).^2-p*u.*(u-1)*k0.^(u-1)./2).*t.^(3*a)/gamma(3*a+1));
% grid
%t = linspace(0,0.1);
%u = linspace(0.3,0.9);
%[T,U] = meshgrid(t,q);
t = linspace(0,0.1,50);
a = linspace(0.3,0.9,50);
[T,A] = meshgrid(t,a);
% evaluate function
Z = k(T,A);

Unrecognized function or variable 'a'.

Error in solution>@(t,u)(k0+(p*k0.^u-q*k0).*t.^a/gamma(a+1)+(p*k0.^u-q*k0).*(p*u*k0.^u-q).*t.^(2*a)/gamma(2*a+1)+(p*k0.^u-q*k0).*((p*u*k0.^u-q).^2-p*u.*(u-1)*k0.^(u-1)./2).*t.^(3*a)/gamma(3*a+1)) (line 6)
k = @(t,u) (k0 + (p*k0.^u-q*k0).*t.^a/gamma(a+1) +(p*k0.^u-q*k0).*(p*u*k0.^u-q).*t.^(2*a)/gamma(2*a+1)...

% plot
figure
surf(T,A,Z)
%surf(T,Q,Z,'facecolor','none')
xlabel('t');
ylabel('\mu');
zlabel('k(t)')

Answer 1

[Cris LaPierre]

You create an anonymous function, k, that uses a variable a in the function. However, this variable was not defined at the time the anonymous function was defined.

[Cris LaPierre]

Perhaps you meant to define a=0.6 instead of u?

% param value
% p is constant and q varies
k0 = 0.0000169; a=0.6; p=536.2; q=0.0000376;
% your function
 k = @(t,u) (k0 + (p*k0.^u-q*k0).*t.^a/gamma(a+1) +(p*k0.^u-q*k0).*(p*u*k0.^u-q).*t.^(2*a)/gamma(2*a+1)...
  +(p*k0.^u-q*k0).*((p*u*k0.^u-q).^2-p*u.*(u-1)*k0.^(u-1)./2).*t.^(3*a)/gamma(3*a+1));
% grid

t = linspace(0,0.1,50);
u = linspace(0.3,0.9,50);
[T,A] = meshgrid(t,u);
% evaluate function
Z = k(T,A);
% plot
figure
surf(T,A,Z)

xlabel('t');
ylabel('\mu');
zlabel('k(t)')

[Mathew]

Here is exactly the code that I wanted to run.

The code does not produce an image with MATLAB 2023b.

Warning: Matrix is singular to working precision.

% Warning: Matrix is singular to working precision.
% That is the response that I get. 
% param value
clear all; close all;
% p is constant and q varies
k0 = 0.0000169; u=0.6; p=536.2; q=0.0000376;
 k = @(t,a) (k0 + (p*k0.^u-q*k0).*t.^a/gamma(a+1) +(p*k0.^u-q*k0).*(p*u*k0.^u-q).*t.^(2*a)/gamma(2*a+1)...
  +(p*k0.^u-q*k0).*((p*u*k0.^u-q).^2-p*u.*(u-1)*k0.^(u-1)./2).*t.^(3*a)/gamma(3*a+1));
% grid
t = linspace(0,1,50);
a = linspace(0.25,0.85,50);
[T,A] = meshgrid(t,a);
% evaluate function
Z = k(T,A);

Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 4.818625e-53.

Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 1.825871e-53.

Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 6.413452e-54.

% plot
figure
surf(T,A,Z)
xlabel('t');
ylabel('\alpha');
zlabel('k(t)')

[Steven Lord]

You likely want to use array division (element-wise) rather than matrix division.

% p is constant and q varies
k0 = 0.0000169; u=0.6; p=536.2; q=0.0000376;
 k = @(t,a) (k0 + (p*k0.^u-q*k0).*t.^a./gamma(a+1) +(p*k0.^u-q*k0).*(p*u*k0.^u-q).*t.^(2*a)./gamma(2*a+1)...
  +(p*k0.^u-q*k0).*((p*u*k0.^u-q).^2-p*u.*(u-1)*k0.^(u-1)./2).*t.^(3*a)./gamma(3*a+1));
% grid
t = linspace(0,1,50);
a = linspace(0.25,0.85,50);
[T,A] = meshgrid(t,a);
% evaluate function
Z = k(T,A);
% plot
figure
surf(T,A,Z)
xlabel('t');
ylabel('\alpha');
zlabel('k(t)')

[Mathew]

Thanks @ Steven Lord and @ Cris LaPierre