Recommended Free Mathematics Software

[hypermorphism]

What free mathematics software do you use regularly or recommend for uniqueness ?
I use http://www.cs.ubc.ca/nest/imager/contributions/scharein/KnotPlot.html for quick graph checks or trivial numeric evaluation/integration. That it allows easy mouse-controlled rotation of 3-d surfaces is a welcome bonus.
What do you recommend ?

Edit: Whoops. Moderators feel free to move this to software.

 

[bomba923]

GraphCalc is good, but what if I want a conditional interval for my 3D graph?
For example, for $$y\left( {x,z} \right) = z\cos \left( {zx} \right)$$ , suppose I want to restrict the 3D image for values of x and z that will satisfy $$\left| {zx} \right| \leqslant \frac{\pi }{2}$$

I can modify a window, but what if I want to set up this conditional interval ? (see Only the x and z values satisfying the condition, not the rest of the graph)

 

[hypermorphism]

GraphCalc is good, but what if I want a conditional interval for my 3D graph?
For example, for $$y\left( {x,z} \right) = z\cos \left( {zx} \right)$$ , suppose I want to restrict the 3D image for values of x and z that will satisfy $$\left| {zx} \right| \leqslant \frac{\pi }{2}$$

I can modify a window, but what if I want to set up this conditional interval ? (see Only the x and z values satisfying the condition, not the rest of the graph)

Check out this page, and note that your equation under your condition can be translated to z(x,y) = y*cos(y*x)*(abs(x*y) <= (Math|pi)/2) .