Back-calculating a variable in equation to give a value of zero

I have a non linear equation with many variables that run through a column array. I am trying to backcalulate the value of one of the variable that would produce a value of zero at each output of the column array. I am using root2d function, which is working fine, but I am only getting the last value. I am not sure how to save the output at each increment of j because the function runs througha for loop and doesn't stop till the last value. I would like the output of my variable rd to be spit out as a column or row array for each increment. Here is what I am doing:

%Calling the function
fun =@root2d;
rd0 = [0.05];
rd = fsolve(fun,rd0)

%loading input and defining variables
function F=root2d(rd)

load 'S71'
depr1=S71.Depth;
qdynr=S71.qdyn;
Velr=S71.velr;
dec2r=S71.dec;
phicv=34;
Q=6;
R=1;
V50=1;
Nkt=12;
c0=300;
c1=0.46;
c2=2.96;
gammap=8;   %in kN/m3
k0=0.5;
chmin=0.031; 

%for loop inside the function
for j=9:numel (depr1)  
    pm(j)=gammap*((1+2*k0)/3)*depr1(j);
    V(j)=(Velr(j)*0.04375)/chmin;
    strainterm(j)=1/(1+(V(j)/V50));
    pm (j)
    strainterm(j)
    V(j)
    qdynr(j)

F= qdynr(j)-(((Nkt*0.5*((6*sin(phicv))/(3-sin(phicv)))*exp(Q-1/rd)))+strainterm (j)*((((c0*(pm(j)^c1)*exp(rd*c2))-(Nkt*0.5*((6*sin(phicv))/(3-sin(phicv))))*exp(Q-1/rd)))));
end
end

[Paresh yeole]

please format your code in order to make it readable..

https://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup#answer_18099

Answer 1

[Paresh yeole]

k = 1; % outside the loop
% inside the loop
F(k) = ... %rest remains unchanged 
k = k+1;    

[madhan ravi]

XD, it’s always a good idea to preallocate.

[Paresh yeole]

The whole point of answering almost the same thing was to put the point that instead of using a cell array, try using an array..

And yes you are correct, preallocating is a good idea.

[Reem Jaber]

Well, thanks guys! I have tried doing that before but it didn't work. Once I index F with k, the solution doesn't work anymore. I have attached the data file for your reference.

Answer 2

[madhan ravi]

 % outside the loop
 F = cell(9:numel(depr1), 1);
 k = 0;

 % inside the loop
 k = k + 1; % the first line
 F{k} = ... rest remains unchanged

[Reem Jaber]

Thank you! But it doesn't seem to be working, I think the problem is in F{k), it is resulting in an error in the fsolve: "FSOLVE requires all values returned by functions to be of data type double". Also, the size of the cell is resulting in an error too once I define it as you did, it worked when I changed into a scalar.

[madhan ravi]

I can’t help because I don’t have your data