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I have a function f(x) and just want to plot log f(x) against log x. This is common in chemistry and biochemistry. It should have been easy.

I have picked up several graphing apps but they would not do it.

In the past when I occasionally needed to do this I managed with making variable 10^x or 10^-x and ugly acrobatics. It would be better to do it by a Parametric plot, and have x = log u, y = log f(u).

Whichever way you do it the trouble is the great variation in the step size. At least I think that is why it is not working. I think I may have got away with it earlier because there was not such variation of x as in my present problem, but now I need to cover at least five orders of magnitude. I think what is happening is my apps are graphing me from log x = 0 to -2 but then the whole range from -2.5 to -6 is smaller than a single step. If I made the step size small enough for that range, then it would take for ever to cover the larger range.

Anyway with the apps I have it is difficult or impossible to control the step size.

I have Free Graphing Calculator by William Jockusch. This does have parametric plotting and does havestep size control - which I found once and can't find again Nice colours. Can only do four graphs but that is okay.

Have Quick Graph. More colours, more graphs, better memory, but does not have parametric that I can see.

Have a Wolfram Alpha app,, I did manage to plot the function using the 10^-x wheeze and it looks exactly as I predict, but has no nice graphics, and I wanted to put two simple (asymptote) lines on it, don't know how and saving is awkward. Did not manage to get Wolfram Alpha log plots or parametric to work at all.

Can you recommend anything? Simple to use, I really don't want to spend much time mastering complicated instructions - or lack of instructions! For the moment this is just for one homework question answer, so can't spend much time, though it will be useful in the future