WHY do i get Error "Undefined function or variable"

As part of my code i run a while loop over a period of time defined and within it have this if loop which produces the array for xcounter, however if i try and use xcounter outside of the 'if' loop it says it is undefined?

Here is an extract of my code relevant to this and below it is the function file for counter;

time=0; %Initialise time
dt=0.01; %Define time step
tfinal=40;
diagstep=10; %define step size for diagnostic
diagcounter=0;

while time<tfinal

if ((round([time/diagstep]) * time) == time) 

         [xcounter] = ParticleCounterFun(x0, particleno)   
         diagcounter=diagcounter+1;
  end
        xcounter
  end

The function file 'ParticleCounterfun' is as follows

function [ xcounter ] = ParticleCounterFun( x0, particleno )

%Initialise counters used in E field diagnostics

counter01=0;

counter12=0;

counter23=0;

counter34=0;

counter45=0;

    for np=1:particleno

         if 0<=x0(np) & x0(np)<1
             counter01=counter01+1;
         end
         if 1<=x0(np) & x0(np)<2
             counter12=counter12+1;
         end
         if 2<=x0(np) & x0(np)<3
             counter23=counter23+1;
         end
         if 3<=x0(np) & x0(np)<4
             counter34=counter34+1;
         end
         if 4<=x0(np) & x0(np)<5
             counter45=counter45+1;
         end

     end
     xcounter=[counter01 counter12 counter23 counter34 counter45];
  end

Can someone tell me why when i run it matlab says;

>> ParticlePusher
Undefined function or variable 'xcounter'.

Error in ParticlePusher (line 100)
   xcounter

Thank You!

[Star Strider]

It’s difficult for me to figure out what you’re doing, but it seems to me you could eliminate ParticleCounterFun altogether by using histc.

Answer 1

[Mischa Kim]

Phoebe, I assume that your code never enters the if-construct. If you remove the semi-colon from

 diagcounter=diagcounter+1

do you see the value for diagcounter being displayed in the MATLAB command window? If not, the code does not enter the if-construct, xcounter does not get a value assigned and that's probably why you get the error msg.

[Phoebe]

i can output xcounter so i know it has value;

xcounter = 1 3 3 2 0

which i know is correct. I can output xcounter from the function file or outside my while loop to give me the very last number so I can not see why it will not output when i have just exited the if loop but still within the while. I can output diagcounter but it prints as 0 so do you think this means it does not enter the loop?

Ive tried a larger tfinal with a smaller diagstep (e.g. tfinal=60, diagstep=5) and still the same so in theory it should? Thanks in advance

[Phoebe]

Hi you are right I dont think it does enter my if loop but i cannot see why as if the time goes up to 40 and my diagstep is 10 you would expect to?

time=0; %Initialise time

tfinal=40;

diagstep=10;

diagcounter=0;

while time<tfinal

 if ((round(time/diagstep) * diagstep) == time)

       [xcounter] = ParticleCounterFun(x0, particleno) 

       diagcounter=diagcounter+1

   end

Where the xcounter function file is;

function [ xcounter ] = ParticleCounterFun( x0, particleno )

%Initialise counters used in E field diagnostics

counter01=0;

counter12=0;

counter23=0;

counter34=0;

counter45=0;

for np=1:particleno
     if (0<=x0(np)) & (x0(np)<1)
         counter01=counter01+1;
     end
     if (1<=x0(np)) & (x0(np)<2)
         counter12=counter12+1;
     end
     if (2<=x0(np)) & (x0(np)<3)
         counter23=counter23+1;
     end
     if (3<=x0(np)) & (x0(np)<4)
         counter34=counter34+1;
     end
     if (4<=x0(np)) & (x0(np)<5)
         counter45=counter45+1;
     end

   end
   xcounter=[counter01 counter12 counter23 counter34 counter45]

end

[Mischa Kim]

Phoebe, there are a couple of issues (see code and comments). You probably have to fine-tune the code to make it do exactly what you want it to do. This should do, for now:

function test_fun()

time=0; %Initialise time
tfinal=40;
diagstep=10;
diagcounter=0;
xcounter = [];                     % initialize xcounter
x0 = [1 2 3];                      % random x0
particleno = 3;                    % random particleno
while time<tfinal
  if ((round(time/diagstep) * diagstep) == time)
    xcounter    = ParticleCounterFun(x0, particleno)
    diagcounter = diagcounter+1
  end

    time = time + tfinal/diagstep; % update time for loop
  end
  end                              % end of test_fun()

function [ xcounter ] = ParticleCounterFun( x0, particleno )

counter01=0;
counter12=0;
counter23=0;
counter34=0;
counter45=0;

for np=1:particleno
  if (0<=x0(np)) & (x0(np)<1)
      counter01=counter01+1;
  end
  if (1<=x0(np)) & (x0(np)<2)
      counter12=counter12+1;
  end
  if (2<=x0(np)) & (x0(np)<3)
      counter23=counter23+1;
  end
  if (3<=x0(np)) & (x0(np)<4)
      counter34=counter34+1;
  end
  if (4<=x0(np)) & (x0(np)<5)
      counter45=counter45+1;
  end
end
xcounter=[counter01 counter12 counter23 counter34 counter45];
end                                % end of PCF function

Answer 2

[Walter Roberson]

Perhaps you wanted

if ((round([time/diagstep]) * time) == time)

to be

if ((round([time/diagstep]) * diagstep) == time)

[Phoebe]

yes that is correct and I have amended it although the same error still appears?