Operator '*' is not supported for operands of type 'function_handle'.

clc; clear all; 
format compact; format long e;
set(0,'defaultaxesfontsize',16.5,'defaultaxeslinewidth',0.8,...
    'defaultlinelinewidth',2.0,'defaultpatchlinewidth',2.7,...
    'defaultaxesfontweight','Bold')

b=0.4;c=11;d=6;e=130;f=10;m=1;
global a 
brange = 5:1:12.2;               
k = 0; tspan = 0:1e-1:70;
xmax = [];                   
for a = brange 
    a
    j = 1; k = k + 1;
    f = @(t,x) [a*x(2)+(0.2+0.2.*abs(x(4))).*x(3);b*((x(4).^2)-13).*x(3)-c*x(2);-d*x(1)-e*x(2)-f*x(3);(x(3).^2)-x(4).^2];
    x0 = [0 0 1 1];                   
    [t,x] = ode15s(f,tspan,x0);    
    count = find(t>10);  
    x = x(count,:); 
    j = 1; 
    n = length(x(:,1));    
    for i=2 : n-1 
        if (x(i-1,1)+eps) < x(i,1) && x(i,1) > (x(i+1,1)+eps)
            xmax(k,j)=x(i,1); 
            j=j+1; 
        end 
    end 
    
    if j>1 
        plot(a,xmax(k,1:j-1),'k.');   
    end 
    hold on; 
    index(k)=j-1; 
end 
xlabel('Bifurcation parameter b'); 
ylabel('x max'); 
title('Bifurcation diagram for b'); 

error is like:

a =

5

a =

6

Operator '*' is not supported for operands of type 'function_handle'.

Error in double_mem_bif>@(t,x)[a*x(2)+(0.2+0.2.*abs(x(4))).*x(3);b*((x(4).^2)-13).*x(3)-c*x(2);-d*x(1)-e*x(2)-f*x(3);(x(3).^2)-x(4).^2] (line 16)

f = @(t,x) [a*x(2)+(0.2+0.2.*abs(x(4))).*x(3);b*((x(4).^2)-13).*x(3)-c*x(2);-d*x(1)-e*x(2)-f*x(3);(x(3).^2)-x(4).^2];

Error in odearguments (line 90)

f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode15s (line 152)

odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

Error in double_mem_bif (line 18)

[t,x] = ode15s(f,tspan,x0);

>>

Answer 1

[Steven Lord]

b=0.4;c=11;d=6;e=130;f=10;m=1;
% ...
f = @(t,x) [a*x(2)+(0.2+0.2.*abs(x(4))).*x(3);b*((x(4).^2)-13).*x(3)-c*x(2);-d*x(1)-e*x(2)-f*x(3);(x(3).^2)-x(4).^2];

Change the name of your anonymous function so it doesn't overwrite the constant f you defined above. Use that new name when you call ode15s.