[Visualpython-users] log-log & semi-log plots

[Gabor K. <Kal...@ms...>]

For semi-log plots:  How can one "fool" Vpython  to display y=f(log10(x)) ? 
See sample program below

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from visual import *
from visual.graph import *

graph1=gdisplay(x=0,y=0, width=400,height=200,title="FFT",xtitle="n-th",
                ytitle="ampl",xmax=20,xmin=0,ymax=200,ymin=0,
                foreground=color.black,background=color.white)
plot1 = gvbars(delta=0.5, color=color.green)


import numarray.fft.fftpack as fftpack
from scipy import *
import math

npts=4096 #Use some power of 2

t=linspace(0,1,npts+1)
dt = (t[-1]-t[0])/(len(t)-1)     # Maximum frequency is 1/dt ? 
fmax = 1/(2*dt)

sig=[]
for i in range(0,npts+1):
    if i<0.5*npts:
        sig.append(100.)
    else:
        sig.append(-100)

#f1 = 400
#sig=2*sin(2*pi*f1*t)+0.5*sin(2*pi*5*f1*t)

ft = fft(sig,n=npts)
coeff=pi*2**(log10(npts)/log10(2)-3)
mgft=abs(ft)/coeff                         )

df = fmax/float(npts/2)
f=(linspace(0,fmax,0.5*npts+1))

for i in range(1,21):
    plot1.plot(pos=(f[i],mgft[i]))
print "done"