MATLAB Answers

My plot is not showing a line? Why?

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Frederick Anokye
Frederick Anokye on 26 Jan 2020
Commented: Walter Roberson on 26 Jan 2020
%Plot of net energy,attractive energy and repulsive energy of a two
%isolated ions seperated by a distance
% r is interatomic distance between the ions
clc; clear;
A=1.436; B=7.32*10^-6; n=8;
r = 0:0.1*10^-9:1*10^-9;
Net_Energy = zeros(length(r),1);
Attractive_Energy = zeros(length(r),1);
Repulsive_Energy = zeros(length(r),1);
for i=1:length(r)
Net_Energy(i) = -A/r(i) + B/r(i)^n;
Attractive_Energy(i) = -A/r(i);
Repulsive_Energy(i) = B/(r(i)^n);
end
for i=1:length(r)
plot(r(i),Net_Energy(i),'g')
hold on
plot(r(i),Attractive_Energy(i),'g')
hold on
plot(r(i)*10^9,Repulsive_Energy(i),'g')
hold on
end

Answers (3)

Walter Roberson
Walter Roberson on 26 Jan 2020
Remove the plotting loop and use
plot(r*10^9,Net_Energy,'g')

Eddie
Eddie on 26 Jan 2020
Replace this
for i=1:length(r)
plot(r(i)*10^9,Net_Energy(i),'g')
hold on
end
with
f=figure; ax=axes(f);
plot(ax,r*10^9,Net_Energy,'g');
If you want to plot a line, the data need to be a single input to plot function instead of using a for loop, which would only plot your data points as individual points.
  2 Comments
Eddie
Eddie on 26 Jan 2020
Remove the for loop, use this instead
plot(r,Net_Energy,'g')
hold on %only need to do it once
plot(r,Attractive_Energy,'g')
plot(r*10^9,Repulsive_Energy,'g')
However, the last plot (Repulsive_Energy) won't appear with the other plots in the same region (since ther previous two plots are in region r, while the last one is in region r*10^9. I suspect this is what you want -
plot(r*10^9,Net_Energy,'g')
hold on %only need to do it once
plot(r*10^9,Attractive_Energy,'g')
plot(r*10^9,Repulsive_Energy,'g')

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Frederick Anokye
Frederick Anokye on 26 Jan 2020
Thanks!
How can I make the lines curvy
  2 Comments
Walter Roberson
Walter Roberson on 26 Jan 2020
use semilogy() instead of plot() to make the lines curvy.
To label the lines, use legend()

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