Output argument "D" (and maybe others) not assigned during call to "E:\PRO\NN​EWPTR\MRG.​m>MRG".

Hi , I am using forth order RK method to solve my probolem.But while calling one subfunction MRG.m to main function i am getting error message

Output argument "D" (and maybe others) not assigned during call to
"E:\PRO\NNEWPTR\MRG.m>MRG".

I have tried by using link http://www.mathworks.com/matlabcentral/answers/97825-why-do-i-get-the-error-output-argument-variable-and-maybe-others-not-assigned-during-call-t but unable to solve it.

here is the code of MRG.m

function [D]= MRG(p_cp,p_t)
rho=2.389;
drg=.032;
dh=.04E-3;
lrg=.8;
mu=15.21E-6;
phi=.7;
r=2074;
t1=(rho*pi*drg*drg*dh*dh)/(600*lrg*mu);
t2=(phi*phi*phi)/(1-phi);
if(p_cp>p_t)
   D=t1*t2*(p_cp-p_t);
elseif(p_cp>p_t)
   D=t1*t2*(p_t-p_cp);
elseif(p_cp==p_t)
   D=0;
end

The main function code which is related to this function is

for m=1:1:100
    v_cp=vo+(0.5*vs*(1+sin(omega*t(m))));
    v_cpdot=vs*pi*f*cos(omega*t(m));
    m_o=MO(p_t(m),p_r(m));
      m_rg=MRG(p_cp(m),p_t(m));
end,

Actually it is a part of code of main function,I have not attached the detailed code becz it will be difficult to understtod if required i will send.

plz help...............

Answer 1

[Geoff Hayes]

Debashis - if you put a breakpoint in your function MRG, call it, and then step through the code using the debugger you will probably find that none of the conditions in the if and elseif block are satisfied, and so D is never instantiated...hence the error that the output parameter D is not assigned any value.

The first line of MRG should initialize this value (and any other output values if they exist) to some default value. In this case,

 D = [];

would be sufficient. This will solve the problem given by the error message, but it will not solve the why none of the conditions are being satisfied. Again, use the debugger to make sure that the provided inputs make sense and that the conditions make sense too. I suspect the problem is with your second condition which is the same as the first

 if(p_cp>p_t)
   D=t1*t2*(p_cp-p_t);
 elseif(p_cp>p_t)
   D=t1*t2*(p_t-p_cp);

The second condition should probably be

 elseif(p_cp<p_t)

(just swap the greater than to a less than).

[DEBASHIS PANDA]

Thankyuou very much sir , Actually i have modeled the equation like (p_cp<p_t),unfortunately while typing i have typed wrong,thankyou onceagain....

[Image Analyst]

That was not the problem of the error. The problem was that if none of the 3 conditions in your if/else were satisfied, D would never get assigned a value. You can assign it null, like Geoff showed you as soon as you enter the function, before the if/else, and that will solve the problem.