Why will my function not run?

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James Crowe
James Crowe 2017-11-20
评论： Walter Roberson 2020-12-18
Hi all, why will my function not run? If p = 1 I want to find the determinant of A, if p = 2 I want to find the trace of A and if p doesn't equal 1 or 2 I want to display the error message. Is my code correct, or is there a better way to do it? And why does the function not run. Thank you!
function [det(A),tr(A)] = myFunction(A,p)
if p == 1
det(A) = det(A);
elseif p == 2
tr(A) = trace(A);
else
disp ('Invalid input')
end

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采纳的回答

Walter Roberson
Walter Roberson 2017-11-20
function [detA,trA] = myFunction(A,p)
if p == 1
detA = det(A);
elseif p == 2
trA = trace(A);
else
disp ('Invalid input')
end
However, you are going to have the problem that in each case you are not assigning to one of the output variables. You should check: does the assignment expect you to return the two possibilities to different variables or to just one output?
function result = test(something)
if something == 1
result = 15;
elseif something == 2
result = -10;
else
result = 'What?'
end
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Vlad Atanasiu
Vlad Atanasiu 2020-12-18
So: If any outputs of a function are undefined, then Matlab throws an error.
Write a function were the first outputs are not defined:
function [a,b,c] = undefined_output(x)
c = x;
Call the function:
try
[a,b,c] = undefined_output('no error');
disp(c)
catch
disp('error')
end
Answer:
error
Where is this behavior specified in the Matlab documentation?
Walter Roberson
Walter Roberson 2020-12-18
Ran in:
Not exactly correct. There is only an error if an unassigned output position is assigned to a variable or used in an expression.
try
[a,b] = undefined_output('no error c unused');
disp(b)
catch
disp('error')
end
b okay
try
[a,b,c] = undefined_output('no error c');
disp(b)
disp(c)
catch
disp('error')
end
error
function [a,b,c] = undefined_output(x)
a = x;
b = 'b okay';
end

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