# How to shade region under a mathematical curve?

I want to show the effect of threshold on FAR and FRR( basically the region under a curve with when the x-range is bounded ). To do that I need to do something like this!! image

If the threshold is changed so does the values. I have to illustrate similar concepts and so have to draw a lot of similar curves and do some basic effects( using colour ) on the curve. Now this is not exactly a mathematical function. Also it is not much useful to plot these values after gathering data. Is there some graphic tool( possibly free ) that I can use to draw this type of general graphs. Is there a way or do I need to write code( python matplot/octave ) to do this?

-
check with mathematica.stackexchange.com. I think Matematica is expensive, but the people there (I am certain) know about alternatives. – horatio Nov 21 '12 at 17:54

I think you are saying you want to draw arbitrary freehand curves yourself, rather than plotting a mathematical function.

If so, for best results, you should be looking at a vector-based drawing application, such as Inkscape (free) or Illustrator (commercial), rather than a raster/pixel-based image editing application like Gimp.

If you do want to plot a precise mathematical function, you need to start with a graphing/charting application instead, but a recommendation is probably out of scope for this site. Illustrator does have very basic charting abilities, but they are generally used for bar and pie charts.

You might also benefit from a hybrid workflow: start by using a graphing/charting application and edit/overlay/annotate its output in Inkscape.

-

OmniGraphSketcher is great, but not free. http://www.omnigroup.com/products/omnigraphsketcher/overview/

It sounds like it might be the kind of thing your after. Works with freehand drawn curves or data, looks great and can export to a variety of formats. OS X only though.

If you do end up writing your own solution, using a library like Highcharts might be a good approach?

http://www.highcharts.com

-