Plotting a loop in MATLAB - matlab

Question

I am very new to MATLAB and am struggling to plot my data. In the program below I have modelled a relation between water level (m.a.s.l) and volume of water captured in a tank. Now I need to plot it in a way that H (water level) be in the Y-axis and V (Volume of the water) be in x-axis. However I have read a lot and tried a lot but still couldn't figure it out. Can Someone Help me PLS ??
I have tried to use simple Plot (X,Y) but it gives error. And so many other suggestions. I also tried fprintf function to have it a s a table in txt then plot it on Excel but always printed the last two H and V. not all of them.
for H = 410.03:0.01:414.57
L = 30; v = 0; fun1 = #(x) (0.3.^2-x.^2).^0.5;
if (H<410.03)
%For the heights below the tank, section 0
dis('No Water in the tank')
elseif (H>=410.03 && H<=410.33)
%section (1)
h = .3-(H-410.03) ;
a = (0.3.^2-h.^2).^0.5 ;
A = 2*(integral(fun1,0,a)-h*a);
V = A*L ;
disp(['H= ' num2str(H)])
disp(['V= ' num2str(V)])
elseif (H>410.33 && H<=410.38)
% section (1+2)
h = H-410.33 ;
V1 = L*(2*(integral(fun1,0,0.3)-0));
V = V1+(.6*h+22*h.^2)*L ;
disp(['H= ' num2str(H)])
disp(['V= ' num2str(V)])
elseif (H>410.38 && H<=414.57)
h = H - 410.38;
V1 = L*(2*(integral(fun1,0,0.3)-0));
V2 = V1+(0.085)*L;
V = V2 + (2.8*h)* L ;
disp(['H= ' num2str(H)])
disp(['V= ' num2str(V)])
end
end

Answer 1

This might get you started, although what I did here might not be the easiest first step to understand. I made a function H->V out of your code that can take a vector of values H and returns a vector V, suitable for plotting. If you want, you could make a simpler function that looks more like your original (with if-then-else structure) and takes a scalar H and returns a scalar V. Then you could loop over the range of H, creating V step-by-step.
First save a function like this (call the file somefunc.m):
function V = somefunc(H)
% constants
L = 30;
fun1 = #(x) (0.3.^2-x.^2).^0.5;
% set up return value (vector)
V = zeros(size(H));
% Section 1 (pick out the parts of H where it's within the first range)
section1 = find(H>=410.03 & H<=410.33);
h = .3-(H-410.03);
a = (0.3.^2-h.^2).^0.5 ;
% Have to loop here because integral won't take a vector of bounds
for i = section1
A(i) = 2*(integral(fun1,0,a(i))-h(i)*a(i));
end
V(section1) = A(section1)*L ;
% Section 1+2
section_1plus2 = find(H>410.33 & H<=410.38);
h = H-410.33 ;
V1 = L*(2*(integral(fun1,0,0.3)-0)); % scalar
V(section_1plus2) = V1+(.6*h(section_1plus2)+22*h(section_1plus2).^2)*L ;
% Section 3
section3 = find(H>410.38 & H<=414.57);
h = H - 410.38;
V1 = L*(2*(integral(fun1,0,0.3)-0)); % scalar
V2 = V1+(0.085)*L; % scalar
V(section3) = V2 + (2.8*h(section3))* L ;
Then you can run it like this:
H = 410.03 : 0.01 : 414.57;
V = somefunc(H);
plot(H,V);
xlabel('H')
ylabel('V')
I'd avoid having similarly named variables, especially the ones that are distinguished just by upper/lowercase.