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

I need help, I have this error " Output argument "y" (and maybe others) not assigned during call to"

function y=f(t)
d=2;
dstep=0.5; 
T1=606;   
 if (t< T1) | (t>=T1+42)
     y=0;
  else 
      for i=0:5
           if     (T1+i*7<=t)         & (t<=T1+i*7+dstep)
                y=d;
           elseif (T1+i*7+dstep<t)    & (t<T1+i*7+1)
                y=0;
           elseif (T1+i*7+1<=t)       & (t<=T1+i*7+1+dstep)
                y=d;
           elseif (T1+i*7+1+dstep<t)  & (t<T1+i*7+2)
                y=0;
           elseif (T1+i*7+2<=t)       & (t<=T1+i*7+2+dstep)
                y=d;
           elseif (T1+i*7+2+dstep<t)  & (t<T1+i*7+3)
                y=0;
           elseif (T1+i*7+3<=t)       & (t<=T1+i*7+3+dstep)
                y=d;
           elseif (T1+i*7+3+dstep<t)  & (t<T1+i*7+4)
                y=0;
           elseif (T1+i*7+4<=t)       & (t<=T1+i*7+4+dstep)
                y=d;
           elseif (T1+i*7+4+dstep<t)  & (t<T1+i*7+7)
                y=0;
           end
      end
 end

[per isakson]

I fail to reproduce the error you report. How did you call f() to get this error?

However, I got another error

>> f(610)
Undefined function or variable 't0'.
Error in f (line 19)
            elseif (T1+i*7+2+dstep<t)  & (t<t0+i*7+3) 

What should t0 be?

[per isakson]

Proposal: Add an else-block to the if, elseif, else, end construct, e.g.

else
    y = nan;
    

That's a poor proposal. (Still I've been tought there shall always be an else-block.)

[B.E.]

Sorry

[per isakson]

Now I'm able to run the code, but I fail to make it throw an error.

How did you call f() to get this error? What input did you use to get the error?

[B.E.]

I have two problems

when

 t=0:0.25:700 % N=length(t)=2801
 y=f(t)

I have this error

Output argument "y" (and maybe others) not assigned during call to

 fplot(@(t) f(t),[0 700],2801,'.-.r')

or

 t=0:.25:700;
 y=zeros(length(t),1);
 for i=1:length(t)
     y(i)=f(t(i));
 end
 plot(t,y)

for the plotting of curve of f, I choose the time step equal to (i.e. iteration) therefore normally but according to the graph below

[per isakson]

Regarding the first problem, did you read and understand my answer?

[B.E.]

I use the version

[per isakson]

Version 7.6 (R208a) supports nonscalar expressions in if-elseif-else according to the documentation.

Answer 1

[David Hill]

y might never get assigned in your function. What do you want y to be if it doesn't meet any of your conditional statements? Just assign y at the beginning (i.e., y=0;)

[Image Analyst]

And change | to ||:

function y = f(t)
y = 0; % Initialize y in case we don't enter the if block.
d=2;
dstep=0.5; 
T1=606;   
if (t < T1) || (t >= T1 + 42)
      y = 0;
else 
      for i = 0 : 5
           if     (T1+i*7<=t)         & (t<=T1+i*7+dstep)
                y=d;
           elseif (T1+i*7+dstep<t)    & (t<T1+i*7+1)
                y=0;
           elseif (T1+i*7+1<=t)       & (t<=T1+i*7+1+dstep)
                y=d;
           elseif (T1+i*7+1+dstep<t)  & (t<T1+i*7+2)
                y=0;
           elseif (T1+i*7+2<=t)       & (t<=T1+i*7+2+dstep)
                y=d;
           elseif (T1+i*7+2+dstep<t)  & (t<T1+i*7+3)
                y=0;
           elseif (T1+i*7+3<=t)       & (t<=T1+i*7+3+dstep)
                y=d;
           elseif (T1+i*7+3+dstep<t)  & (t<T1+i*7+4)
                y=0;
           elseif (T1+i*7+4<=t)       & (t<=T1+i*7+4+dstep)
                y=d;
           elseif (T1+i*7+4+dstep<t)  & (t<T1+i*7+7)
                y=0;
           end
      end
end

But did you notice that y gets overwritten each time in your for loop? So y will end up with whatever y it decides to use for the final i=5 case. All the iterations from 0 to 4 will be ignored because the y for those iterations gets overwritten.

Answer 2

[per isakson]

I found this on if-elseif-else in the documentation of R14.

Nonscalar Expressions

If the evaluated expression yields a nonscalar value, then every element of this value must be true or nonzero for the entire expression to be considered true. For example, the statement if (A < B) is true only if each element of matrix A is less than its corresponding element in matrix B.

Matlab may contain the old code even if is not documented. Backward compatibility for old-timers.

For every elseif expression the Code Analyzer reports

When both arguments are numeric scalars, consider replacing | with || for performance.

I take that as a hint that the old code is still there.

The the documentation of recent releases don't say anything about scalar or nonscalar expressions. It goes without saying that the values of the expressions are scalar. (As far as I can see.)

The call f([606:609]') reproduces the error you report.

Output argument "y" (and maybe others) not assigned during call to "f>f_".
Error in f (line 7)
y = f_([606:609]')

Your expressions, e.g. (T1+i*7+dstep<t), are noncalar when f() is called with a vector.

What Matlab release are you using?

How did you call f() ?