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  • log log scale scatterplot

    From sid@21:1/5 to All on Tue Dec 5 10:21:22 2017
    Hello all,
    I need to plot in log log scale and it is a scatter plot and I need to get the slope and intercept after fitting with linfit. This needs to be plotted in logarithmic space. And also the correlation coefficient needs to be calculated in log-log
    space.

    I have 10 x values and 10 y values
    is this correct plot, alog10(x), alog10(y)
    or like this plot, x,y,/xlog,/ylog but I need the values in order to find the linfit.

    how to do this
    thanks

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  • From Ben Castellani@21:1/5 to sid on Tue Dec 5 13:49:46 2017
    On Tuesday, December 5, 2017 at 11:21:27 AM UTC-7, sid wrote:
    Hello all,
    I need to plot in log log scale and it is a scatter plot and I need to get the slope and intercept after fitting with linfit. This needs to be plotted in logarithmic space. And also the correlation coefficient needs to be calculated in log-log
    space.

    I have 10 x values and 10 y values
    is this correct plot, alog10(x), alog10(y)
    or like this plot, x,y,/xlog,/ylog but I need the values in order to find the linfit.

    how to do this
    thanks

    x = [1487.,500,24,3455,2233]
    y = [11,50,2400,32.3,111]

    fit = linfit(alog(x),alog(y))
    xfit=[min(alog(x)),max(alog(x))]
    yfit = xfit*fit[1]+fit[0]


    p = plot(alog(x),alog(y),symbol='o',linestyle=6,color='blue',sym_filled=1)
    p2 = plot(xfit,yfit,/overplot)
    t = text(0.5,0.8,/normal,'Y = ' + strtrim(string(fit[1]),2) + ' X + ' + strtrim(string(fit[0]),2),color='red')

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  • From Ben Castellani@21:1/5 to sid on Tue Dec 5 13:34:38 2017
    On Tuesday, December 5, 2017 at 11:21:27 AM UTC-7, sid wrote:
    Hello all,
    I need to plot in log log scale and it is a scatter plot and I need to get the slope and intercept after fitting with linfit. This needs to be plotted in logarithmic space. And also the correlation coefficient needs to be calculated in log-log
    space.

    I have 10 x values and 10 y values
    is this correct plot, alog10(x), alog10(y)
    or like this plot, x,y,/xlog,/ylog but I need the values in order to find the linfit.

    how to do this
    thanks

    Here is a sample code that does what you need it to do:

    ;example data (5 points)
    x = [1487,500,24,3455,2233]
    y = [11,50,2400,32.3,111]

    fit = linfit(alog(x),alog(y))
    xfit=[0:max(alog(x)):max(alog(x))/100.]
    yfit = xfit*fit[1]+fit[0]

    p = plot(alog(x),alog(y),layout=[2,1,1],symbol='o',linestyle=6,color='blue')
    p2 = plot(xfit,yfit,/overplot)

    NOTE: You can use either of your plot techniques. This will just change the actual labels on the axes. One will be just the log powers (it will show 3 for 1000), the other will be the data values in log form (it will show 10^3 for 1000)

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  • From sid@21:1/5 to Ben Castellani on Wed Dec 6 22:42:38 2017
    On Wednesday, December 6, 2017 at 3:19:50 AM UTC+5:30, Ben Castellani wrote:
    On Tuesday, December 5, 2017 at 11:21:27 AM UTC-7, sid wrote:
    Hello all,
    I need to plot in log log scale and it is a scatter plot and I need to get the slope and intercept after fitting with linfit. This needs to be plotted in logarithmic space. And also the correlation coefficient needs to be calculated in log-
    log space.

    I have 10 x values and 10 y values
    is this correct plot, alog10(x), alog10(y)
    or like this plot, x,y,/xlog,/ylog but I need the values in order to find the linfit.

    how to do this
    thanks

    x = [1487.,500,24,3455,2233]
    y = [11,50,2400,32.3,111]

    fit = linfit(alog(x),alog(y))
    xfit=[min(alog(x)),max(alog(x))]
    yfit = xfit*fit[1]+fit[0]


    p = plot(alog(x),alog(y),symbol='o',linestyle=6,color='blue',sym_filled=1)
    p2 = plot(xfit,yfit,/overplot)
    t = text(0.5,0.8,/normal,'Y = ' + strtrim(string(fit[1]),2) + ' X + ' + strtrim(string(fit[0]),2),color='red')

    Thanks a lot for the code.

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