Error : Output argument "y" (and maybe others) not assigned during call to "N".

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Kiran Kumar Asokan
评论： Walter Roberson 2019-9-8
I am currently working on building B spline curves basis function which is a recursive function. I am always getting this error Output argument "y" (and maybe others) not assigned during call to "N". Please let me know how to sort this.
function y = N(k,i,t,m)
%k is the order
%i is the pointer for the control point
%t (knot value) is the parameter used for defining a point on the curve
%m is the knot vector
% for the knot value t to be in between the ti and ti+k
if t < m(1,i+k+1)
if t > m(1,i+1)
if k == 1
y = 1;
end
for h = 2:1:k
y = ((((t - m(1,i+1))/ (m(1,i+h)- m(1,i+1)))* N(h-1,i,t,m)) + (((m(1,i+h+1) - t)/ (m(1,i+h+1)- m(1,i+2)))* N(h-1,i+1,t,m)));
end
else
y = 0;
end
end
end
  1 个评论
Stephen23
Stephen23 2019-9-8
"Please let me know how to sort this."
Use consistent code indentation.
Your code is very badly indented. Badly indented code is one way that beginners hide bugs in their code, by making the logic of the code hard to understand.
Make your code easier to understand by using consistent indexing (e.g. the MATLAB default indexing: select all code text, ctrl+i). Then the reason for your unassigned output is obvious.

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回答（2 个）

Star Strider
Star Strider 2019-9-7
The easiest way is to assign a value to ‘y’ at the outset. It will be re-assigned if the if blocks allow it.
Example —
function y = N(k,i,t,m)
y = NaN;
%k is the order
... rest of the function code ...
end
Walter Roberson
Walter Roberson 2019-9-7
Reformat your code:
if t < m(1,i+k+1)
if t > m(1,i+1)
if k == 1
y = 1;
end
for h = 2:1:k
y = ((((t - m(1,i+1))/ (m(1,i+h)- m(1,i+1)))* N(h-1,i,t,m)) + (((m(1,i+h+1) - t)/ (m(1,i+h+1)- m(1,i+2)))* N(h-1,i+1,t,m)));
end
else
y = 0;
end
end
Notice that the else is associated with the inner if t > m(1,i+1) and so is not invoked in the case where t < m(1,i+k+1) is false. Therefore if t < m(1,i+k+1) is false, nothing is assigned to y.

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