Python plotting with for loop

Question

I am a newbie in python and plotting stuff. I was trying to generate a plot using the following script. The goal was to draw a plot of Q vs F for all values.

from pylab import *

n = 5
D = 13
B = 10

x = linspace(-6.5, 6.5, 1000)
y = 1/sqrt(2*pi)*exp(-(x)**2/2)

for i in range(1,n):
    F = sum(y*cos(2*pi*i*x/D)*exp(-i**2*B/(4*D**2)))
    print F

for j in range(1,n):
    Q = 2*pi*(j)/D
    print Q

plt.plot(Q,F,'rx')
plt.show()

When I am running the script, it plots only one data point instead of all. I am sure, I did some stupid mistake. Someone could pls help me out here? Thank you.

will · Accepted Answer · 2013-02-21 13:46:19Z

2

It's because you're setting F and Q equal to the value on each loop, rather than appending the value to the end of an array.

from pylab import *

n = 5
D = 13
B = 10

x = linspace(-6.5, 6.5, 1000)
y = 1/sqrt(2*pi)*exp(-(x)**2/2)

F,Q = [],[]

for i in range(1,n):
    F.append(sum(y*cos(2*pi*i*x/D)*exp(-i**2*B/(4*D**2))))
    Q.append(2*pi*(j)/D)

plt.plot(Q,F,'rx')
plt.show()

answered Feb 21, 2013 at 13:46

will

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Comments

John Lotacs · Accepted Answer · 2013-02-21 13:45:45Z

1

You are only setting Q, F equal in the loops.

from pylab import *

n = 5
D = 13
B = 10

x = linspace(-6.5, 6.5, 1000)
y = 1/sqrt(2*pi)*exp(-(x)**2/2)

for i in range(1,n):
    F.append(sum(y*cos(2*pi*i*x/D)*exp(-i**2*B/(4*D**2))))
    print F
    Q.append(2*pi*(j)/D)
    print Q

plt.plot(Q,F, 'rx')    
plt.show()

answered Feb 21, 2013 at 13:45

John Lotacs

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3 Comments

John Lotacs Over a year ago

I'm not familiar with pylab, I didn't know it plotted lists.

will Over a year ago

It's just standard matplotlib.

user2095624 Over a year ago

Thank you for your help. Now I know what went wrong and learn about it.

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