How can I store data from a nested for loop?

Hello guys, I'm new to this website. I need help with the following problem. I would like to store the values of V and P in two vectors so that I can plot them afterwards. As you can see, in the first loop, I vary the parameter "P1" three times because I have to obtain the values at +/- 25 percent of the original value of P1. As a result, this affects the values of V and P. Thus, since I'm changing the value of P1 three times, I should get three different values for V and P. With these three values (i.e., V = [ a b c] and P = [f g h], I want to construct a V vs P plot. Can someone help me how to do this? I keep getting the error: "in an assignment A(I) = B, the number of elements in B and I must be the same"(please run the code I have attached, thank you). The code seems to work at the beginning but then it stops. Thanks in advance!

P2 = 680;
H = 125;
A = 8;
B = 15;
C = 5.2;

% initial guesses
P(1) = 50; % pressure
V(1) = 80; % flow rate
eps = 0.00001;

for i = 1:3
    P1(i) = 225+450.*0.25.*i;
    for j = 1:50
    v1 = sqrt((P1(i)-P)/A)+sqrt((P2-P)/B)-V;
    p1 = H+C*(V.^2)-P;
    b = v1.^2+p1.^2;

      % check for convergence
      if b<eps
          disp('the required solution is: ')
          fprintf('The flow rate is V = %.4f    The pressure P = %.4f\n',V(i),P(i))
          disp(' ')
          break
      end

      % calculate partial derivatives
      vv = -1;
      vp = (1/2)*(((P1(i)-P)/A).^(-1/2))*(-1/A)+(1/2)*(((P2-P)/B).^(-1/2))*(-1/B);
      pv = 2*C*V;
      pp = -1;
      d = vv.*pp-vp.*pv;
      % determine the increments
      dv = (-v1.*pp+p1.*vp)/d;
      dp = (-p1.*vv+v1.*pv)/d;
      % calculate the values of v and p for next iteration
      V(i) = V+dv;
      P(i) = P+dp;
      % print results
      fprintf('P1 = %.4f\t  V = %.6f\t P = %.6f\n',P1(i),V(i),P(i))
      end
  end

[CS Researcher]

Check the following:

 V(i) = V + dv

V(i) is a scalar while V becomes a vector. Same for P(i)

Answer 1

[Star Strider]

I ran your code but encountered problems with ‘dv’ and ‘dp’ being matrices. I can’t figure out what you want to do with those variables, so I suggest you check the sizes of your various variables and code them to be what you want.