Making curves reach axes

I am trying to make a plot of the power generated by a rising helium balloon in function of its hight for different balloonvolumes. The curves of the smallest 2 balloons dont go all the way down to zero on the plot (or reach the x-axis) wich makes them akwardly float. I tried to modify the y-axis range but it doesn't work.

Vb0_vec = [10 100 250 1000];

mb_vec = (20*10^-3)*(36*pi*Vb0_vec.^2).^(1/3);

lambda = 0.0173;

rhog0 = 0.169;

Cw = 0.41;

y = linspace(0, 11000, 2000);

% Plot 4: vermogen ifv de hoogte voor vershillende ballonvolumes

P_10 = Power(y, Vb0_vec(1), lambda, mb_vec(1), rhog0, Cw);

P_100 = Power(y, Vb0_vec(2), lambda, mb_vec(2), rhog0, Cw);

P_250 = Power(y, Vb0_vec(3), lambda, mb_vec(3), rhog0, Cw);

P_1000 = Power(y, Vb0_vec(4), lambda, mb_vec(4), rhog0, Cw);

figure()

semilogy(y, P_10, 'b-', 'LineWidth', 2)

hold on

semilogy(y, P_100, 'LineWidth', 2)

semilogy(y, P_250, 'r--', 'LineWidth', 2)

semilogy(y, P_1000, 'g:', 'LineWidth', 2)

hold off

ylabel("Vermogen (W)")

xlabel("Hoogte (m)")

title("Momentaan geleverd vermogen over het traject voor verschillende ballonvolumes",...

"FontSize", 16)

legend("10 m³", "100 m³", "250 m³", "1000 m³", "Location", "southeast")

% volgende code zorgt dat de curves mooi doorlopen tot aan de assen

ymin_10 = min(P_10);

ymin_100 = min(P_100);

ymin = max(ymin_10, ymin_100);

ylim = [ymin, 10^5];

xlim([0 11000])

This is the code for the function Power, LoadConstants loads all the necessary parameters/constants:

unction [P] = Power(y, Vb0, lambda, mb, rhog0, Cw)

% vaste parameters

LoadConstants

% tussenberekeningen

% krachten

Fa = rhol0*Vb0*g;

Fzk = lambda*y*g;

Fzb = (rhog0*Vb0+mb)*g;

% hoogteafhankelijke parameters

Vb = Vb0*(1-y*L/Tl0).^(1-(g*Ml/(R*L)));

rhol = rhol0*(1-y*L/Tl0).^((g*Ml/(R*L))-1);

rb = ((3*Vb)/(4*pi)).^(1/3);

Ab = pi*rb.^2;

% vermogen

P = (2/3)*sqrt(2/3)*sqrt(((Fa-Fzb-Fzk).^3)./(Ab*Cw.*rhol));

end

Output of the plot:

Thank you

[Arne]

rhol0 = 1.225;

L = 0.0065;

Tl0 =288.15;

R = 8.314;

g = 9.81;

Ml = 0.02896;

Pl0 =101325;

Cw = 0.285;

[VBBV]

The syntax for ylim function can be referred here

https://www.mathworks.com/help/matlab/ref/ylim.html

Answer 1

[VBBV]

@Arne Those are the smallest values for equations in your program. if you want them to touch the axis, use

ylim([0.1 1e5])

[VBBV]

Vb0_vec = [10 100 250 1000];
mb_vec = (20*10^-3)*(36*pi*Vb0_vec.^2).^(1/3);
lambda = 0.0173;
rhog0 = 0.169;
Cw = 0.41;
y = linspace(0, 11000, 2000);
% Plot 4: vermogen ifv de hoogte voor vershillende ballonvolumes
P_10 = Power(y, Vb0_vec(1), lambda, mb_vec(1), rhog0, Cw);

Cw = 0.2850

P_100 = Power(y, Vb0_vec(2), lambda, mb_vec(2), rhog0, Cw);

Cw = 0.2850

P_250 = Power(y, Vb0_vec(3), lambda, mb_vec(3), rhog0, Cw);

Cw = 0.2850

P_1000 = Power(y, Vb0_vec(4), lambda, mb_vec(4), rhog0, Cw);

Cw = 0.2850

figure()
semilogy(y, P_10, 'b-', 'LineWidth', 2)

Warning: Imaginary parts of complex X and/or Y arguments ignored.

hold on
semilogy(y, P_100, 'LineWidth', 2)

Warning: Imaginary parts of complex X and/or Y arguments ignored.

semilogy(y, P_250, 'r--', 'LineWidth', 2)
semilogy(y, P_1000, 'g:', 'LineWidth', 2)
hold off
ylabel("Vermogen (W)")
xlabel("Hoogte (m)")
title("Momentaan geleverd vermogen over het traject voor verschillende ballonvolumes",...
    "FontSize", 16)
ymin_10 = min(P_10);
ymin_100 = min(P_100);
ymin = max(ymin_10, ymin_100);
%ylim = [ymin, 10^5];
ylim([0.1 1e5])
xlim([0 11000]) 

%ymin_100 = min(P_100);ymin = max(ymin_10, ymin_100);ylim = [ymin, 10^5];xlim([0 11000]) 

function [P] = Power(y, Vb0, lambda, mb, rhog0, Cw)
% vaste parameters
%LoadConstants
% tussenberekeningen
% krachten
rhol0 = 1.225;
L = 0.0065;
Tl0 =288.15;
R = 8.314;
g = 9.81;
Ml = 0.02896;
Pl0 =101325;
Cw = 0.285
%L = 0.0065;Tl0 =288.15;R = 8.314;g = 9.81;Ml = 0.02896;Pl0 =101325;Cw = 0.285
Fa = rhol0*Vb0*g;
Fzk = lambda*y*g;
Fzb = (rhog0*Vb0+mb)*g;
% hoogteafhankelijke parameters
Vb = Vb0*(1-y*L/Tl0).^(1-(g*Ml/(R*L)));
rhol = rhol0*(1-y*L/Tl0).^((g*Ml/(R*L))-1);  
rb = ((3*Vb)/(4*pi)).^(1/3);
Ab = pi*rb.^2;
% vermogen
P = (2/3)*sqrt(2/3)*sqrt(((Fa-Fzb-Fzk).^3)./(Ab*Cw.*rhol));
end% vaste parametersLoadConstants% tussenberekeningen% krachtenFa = rhol0*Vb0*g;Fzk = lambda*y*g;Fzb = (rhog0*Vb0+mb)*g;% hoogteafhankelijke parametersVb = Vb0*(1-y*L/Tl0).^(1-(g*Ml/(R*L)));rhol = rhol0*(1-y*L/Tl0).^((g*Ml/(R*L))-1);  rb = ((3*Vb)/(4*pi)).^(1/3);Ab = pi*rb.^2;% vermogenP = (2/3)*sqrt(2/3)*sqrt(((Fa-Fzb-Fzk).^3)./(Ab*Cw.*rhol));end
%mb_vec = (20*10^-3)*(36*pi*Vb0_vec.^2).^(1/3);lambda = 0.0173;rhog0 = 0.169;Cw = 0.41;y = linspace(0, 11000, 2000);% Plot 4: vermogen ifv de hoogte voor vershillende ballonvolumesP_10 = Power(y, Vb0_vec(1), lambda, mb_vec(1), rhog0, Cw);P_100 = Power(y, Vb0_vec(2), lambda, mb_vec(2), rhog0, Cw);P_250 = Power(y, Vb0_vec(3), lambda, mb_vec(3), rhog0, Cw);P_1000 = Power(y, Vb0_vec(4), lambda, mb_vec(4), rhog0, Cw);figure()semilogy(y, P_10, 'b-', 'LineWidth', 2)hold onsemilogy(y, P_100, 'LineWidth', 2)semilogy(y, P_250, 'r--', 'LineWidth', 2)semilogy(y, P_1000, 'g:', 'LineWidth', 2)hold offylabel("Vermogen (W)")xlabel("Hoogte (m)")title("Momentaan geleverd vermogen over het traject voor verschillende ballonvolumes",...  "FontSize", 16)