MATLAB ploting graph incorrectly, different from same code in Python.
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Rafael Pereira Baptista
on 18 Mar 2021
Answered: the cyclist
on 18 Mar 2021
I'm beggining to learn MATLAB.
I got the following code, but the graph doesn't match the data points when putting the P values manually.
%Pressure
P = 0:1/100:14;
%Parameters Pb
C = 0.55;
alpha = 28.9;
Ba = 0.44;
B = 43.7;
T = 300;
Vr = (1-3*C*alpha*(300-T))*(((P*Ba/B)+1).^-(1/Ba));
K = 2091*(Vr).^0.87;
Theta = 86*((Vr).^-((2.629*(Vr).^(1.2))));
%Resistivity
r = (K*T/(4*(Theta).^2))*(1-(1/18)*(Theta/T).^2+(1/480)*(Theta/T).^4);
r0 = (2091*T/(4*(86).^2))*(1-(1/18)*(86/T).^2+(1/480)*(86/T).^4);
plot(P,r/r0)
I wrote the same code for python and it ploted correctly
from pylab import plot, show, xlabel, ylabel, title
from numpy import linspace
#Pressure
P = linspace(0, 14, 100)
#Parameters Pb
C = 0.55
alpha = 28.9
Ba = 0.44
B = 43.7
T = 300
Vr = (1-3*C*alpha*(300-T))*(((P*Ba/B)+1)**-(1/Ba))
K = 2091*(Vr)**0.87
Theta = 86*((Vr)**-((2.629*(Vr)**(1.2))))
#Resistivity
r = (K*T/(4*(Theta)**2))*(1-(1/18)*(Theta/T)**2+(1/480)*(Theta/T)**4)
r0 = (2091*T/(4*(86)**2))*(1-(1/18)*(86/T)**2+(1/480)*(86/T)**4)
plot(P, r/r0)
xlabel('P(GPa)')
ylabel('R(P)/R(P0)')
title('Pb')
show()
What is wrong with my MATLAB code?
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Accepted Answer
the cyclist
on 18 Mar 2021
In your definition of r, you missed a couple spots that required array operations instead of matrix operations:
%Pressure
P = 0:1/100:14;
P0 = 0.000101325;
%Parameters Pb
C = 0.55;
alpha = 28.9;
Ba = 0.44;
B = 43.7;
T = 300;
Vr = (1-3*C*alpha*(300-T))*(((P*Ba/B)+1).^-(1/Ba));
K = 2091*(Vr).^0.87;
Theta = 86*((Vr).^-((2.629*(Vr).^(1.2))));
%Resistivity
r = (K*T./(4*(Theta).^2)).*(1-(1/18).*(Theta/T).^2+(1/480).*(Theta/T).^4);
r0 = (2091*T/(4*(86).^2))*(1-(1/18)*(86/T).^2+(1/480)*(86/T).^4);
plot(P,r/r0)
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