how do i calculate a 3d graph in this case?

I am trying to draw a graph using the following formula, however i have two vectors instead of a matrices and while the values get calculated, I cannot plot them. I want to plot the graph as pi and pp change.

The code actually calculates the results for all the values, then says there is an error in line 33 without explaining what it is.

Thanks to anyone in advance.

q_wheat=240;
q_iron=12;
q_pig=18;
wheat_totale=450;


q_wheat2=120;
q_iron2=8;
q_pig2=12;
iron_totale=21;

q_wheat3=120;
q_iron3=6;
q_pig3=30;
pig_totale=60;

pw=1;

pi=0.1:0.1:40;
pp=0.1:0.1:40;


for i=1:length(pi)
    for j=1:length(pp)
    
    cost_w(i,j)=q_wheat*pw+(q_iron*pi(i,j))+(q_pig*pp(i,j))
    cost_i(i,j)=q_wheat2*pw+(q_iron2*pi(i,j))+(q_pig2*pp(i,j))
    cost_p(i,j)=q_wheat3*pw+(q_iron3*pi(i,j))+(q_pig3*pp(i,j))

    rev_wheat(i,j)=wheat_totale*pw;
    rev_iron(i,j)=iron_totale*pi(i,j);
    rev_pig(i,j)=pig_totale*pp(i,j)

    prof_iron(i,j)=rev_iron(i,j)-cost_i(i,j);
    prof_wheat(i,j)=rev_wheat(i,j)-cost_w(i,j);
    prof_pig(i,j)=rev_pig(i,j)-cost_p(i,j)

    riron(i,j)=(rev_iron(i,j)/cost_i(i,j))-1
    rwheat(i,j)=(rev_wheat(i,j)/cost_w(i,j))-1
    rpig(i,j)=(rev_pig(i,j)/cost_p(i,j))-1

    end
end
figure(1), plot(pi,riron,pi,rwheat,pi,rpig)

Answer 1

[Image Analyst]

Not exactly sure what you want since you removed all your comments in the code, which I'm sure you put it (like all good programmers do), but this is what I got. Perhaps it's what you intended, perhaps not.

q_wheat = 240;
q_iron = 12;
q_pig = 18;
wheat_totale = 450;
q_wheat2 = 120;
q_iron2 = 8;
q_pig2 = 12;
iron_totale = 21;
q_wheat3 = 120;
q_iron3 = 6;
q_pig3 = 30;
pig_totale = 60;
pw = 1;
pk = 0.1:0.1:40;
pp = 0.1:0.1:40;
for i = 1:length(pk)
    for j = 1:length(pp)
        cost_w(i,j) = q_wheat*pw + (q_iron*pk(i)) + (q_pig*pp(j));
        cost_i(i,j) = q_wheat2*pw + (q_iron2*pk(i)) + (q_pig2*pp(j));
        cost_p(i,j) = q_wheat3*pw + (q_iron3*pk(i)) + (q_pig3*pp(j));
        rev_wheat(i,j) = wheat_totale*pw;
        rev_iron(i,j) = iron_totale*pk(i);
        rev_pig(i,j) = pig_totale*pp(j);
        prof_iron(i,j) = rev_iron(i,j)-cost_i(i,j);
        prof_wheat(i,j) = rev_wheat(i,j)-cost_w(i,j);
        prof_pig(i,j) = rev_pig(i,j)-cost_p(i,j);
        riron(i,j) = (rev_iron(i,j)/cost_i(i,j))-1;
        rwheat(i,j) = (rev_wheat(i,j)/cost_w(i,j))-1;
        rpig(i,j) = (rev_pig(i,j)/cost_p(i,j))-1;
    end
    plot(pk,riron(i, :), 'r-') % Draw iron with a red curve for this i
    hold on
    plot(pk,rwheat(i, :), 'g-') % Draw wheat with a green curve for this i
    plot(pk,rpig(i, :), 'b-') % Draw pig with a blue curve for this i
end
xlabel('pk')
ylabel('iron, wheat, or pig')
% Draw line along x axis
yline(0, 'LineWidth',2);
grid on;

[Cristina Anna Rossi]

Oh thank you! Yes this is what I needed, thank you so much!

I did remove all of my comments because they felt silly, but I will remember to keep them for future questions! I tend to panic a bit using matlab, this has helped me a lot, though, so thank you!

Answer 2

[Torsten]

pi and pp are vectors ; thus trying to access pi(i,j) and pp(i,j) will throw an error.

Further, don't name a variable "pi" in order to avoid conflicts with Ludolph number.

[Cristina Anna Rossi]

thanks a lot, I absolutely did not think of that!

Answer 3

[Can Atalay]

Haven't been able to run your code but I think that your

pi

is a row vector but you're accessing

pi(2,1)

eventually, which doesn't exist.

You could simply access the nth element in a row vector by saying

pi(3)

instead of

pi(1,3)

Moreover, using something along the lines of

ii1, ii2, ii3, etc. / jj1, jj2... / my_pi, pi1, pi_1

instead of

i, j, pi

would be a good idea since these might create some conflict between the inbuilt definitions of "pi" and "i" in MATLAB.

[Cristina Anna Rossi]

oh, thank you so much I absolutely did not think of that!