Difference Between Plots in Idl
I'm Working with Two Plots of Density as a Function of Distance on Idl. What I'd Like to Do with Them Is Convert Them into Plots of Distance as a Function of...
I'm working with two plots of density as a function of distance on IDL. What I'd like to do with them is convert them into plots of distance as a function of density and plot their difference, in order to obtain the shift in distance as a function of density. The issue I'm having is that one of the equations for density as a function of distance is non invertible. Any idea on what I could do to overcome this problem? Thanks in advance. Here are the tewo plots that I'm trying to invert and take the difference of.
lowe = ALOG10(10.)
uppe = ALOG10(170.)
re = DINDGEN(100)*(uppe - lowe)/(100 - 1L) + lowe
r = 10^(re)
loweB = ALOG10(10.)
uppeB = ALOG10(170.)
reB = DINDGEN(100)*(uppeB - loweB)/(100 - 1L) + loweB
rB = 10^(reB)
pl = plot(r,density_r(r), /XLOG, /YLOG)
plB = plot(r,freq_ratB(r), /OVERPLOT, /XLOG, /YLOG)
end
FUNCTION density_r, r
return, 4.8e9/r^14 + 3e8/r^6 + 1.4e6/r^2.3
END
FUNCTION freq_ratB, r
return, 10.*(r/215.)^(-2.8)
END
1 Answer
It is easy to plot distance as a function of density — just change the order of the arguments to plot, i.e.:
p_r = plot(density_r(r), r, /xlog, /ylog)
plB_r = plot(freq_ratB(r), r, /overplot, /xlog, /ylot)
But to subtract the two plots, the x-coordinates of your difference plot must be the same for the two operands of the difference. You can write an equation to invert one of your functions:
; intvert freq_ratB
function r_freq_ratB, density
compile_opt strictarr
return, 215.0 * exp((alog(density) - log(10.0)) / (-2.8))
end
So then you can plot the difference:
p_difference = plot(density, r - r_freq_ratB(density))
If you couldn't invert one of your functions, e.g., you were plotting observational data, then you would have to interpolate.
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