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matlab
TheGeekGreek
TheGeekGreek

Reputation: 169

Computing integral with variable bounds in MATLAB

Consider the following MWE in MATLAB:

f = @(t) integral(@(x) x.^2,0,t);
integral(f,0,1);

This yields the error

Error using integral (line 85) A and B must be floating-point scalars.

(and a bit more). How do I fix this? Is this even possible? I think the problem is the variable upper bound.

Upvotes: 0

Views: 410

Answers (1)

Sardar Usama
Sardar Usama

Reputation: 19689

If you want to use integral then set 'ArrayValued' to true otherwise t would be an invalid end point in integral(@(x) x.^2,0,t). So it would be:

f = @(t) integral(@(x) x.^2,0,t);
integral(f,0,1,'ArrayValued',true)

% ans =
%     0.0833

Alternately, since you're doing double integration, so use the function dedicated for this purpose i.e. integral2. For your example, it would be:

f = @(t,x) x.^2 ;
integral2(f,0,1,0, @(t) t)

% ans =
%     0.0833

If you have Symbolic Math Toolbox, you can also use int as int(expr,var,a,b) but it would be slower. For your case, it would be:

syms x t;
f = x.^2;
req = int(int(f,x,0,t),t,0,1);    % It gives 1/12
req = double(req);                % Convert to double if required

Upvotes: 1

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