loglog graph analyses

hi i have the folowing data i would like to plot in matlab

plotERRLW =

    0.0466    0.0111    0.0074    0.0046

NX =

    50         500        1000        2000

i am using a logarithmic graph to gain a straight line, if i wished to find the gradient of the line would i use the change in the original numbers or change in the numbers after i have taken a log of them?

(also if i have to take a log of them what base does loglog naturally plot)

i have tried a number of options already but can't seem to get the correct answer (i know it should be close to 2) thanks in advance please ask for any more information kyle

Answer 1

[Honglei Chen]

loglog uses 10 based logarithm for both X and Y, so if the resulting figure is a straight line and you want to calculate the slope of that line, you need to take logarithm for both X and Y first.

[kyle lyth]

ahh okay makes a little more sense, however i think there is something wrong with my code as its not produce the answers i am expecting, no worries thanks for your reply :) kyle