Simplifying

*To*: mathgroup at yoda.physics.unc.edu*Subject*: Simplifying*From*: WTG <WTG at corral.uwyo.edu>*Date*: Mon, 1 Jun 1992 15:58 MDT

--QH7TbvXB6itkIG/XESEDvB== Content-type: TEXT --QH7TbvXB6itkIG/XESEDvB== Content-type: TEXT Has anyone encountered, or have any ideas about resolving the following problem? In trying to evaluate symbolically a number of complicated expressions, I have various functions of the following type, In[1]:= f[x_,y_,z_] := Sqrt[m^2 + x^2 + y^2 + z^2] that must be differentiated: In[2]:= D[f[x,y,z], y] y Out[2]= ----------------------- 2 2 2 2 Sqrt[m + x + y + z ] While Mathematica (v 1.2 or v 2.0) recognizes the obvious, In[3]:= D[f[x,y,z], y] == y/f[x,y,z] Out[3]= True it doesn't seem to want to regroup: In[4]:= D[f[x,y,z], y] /. Sqrt[m^2+x^2+y^2+z^2] -> f[x,y,z] y Out[4]= ----------------------- 2 2 2 2 Sqrt[m + x + y + z ] despite considerable effort at variations on this theme. Without being able to contract things like this, and other types of expression, calculations become imposssibly long and cumbersome, and the output is useless. Any hints, ideas, or sympathetic comments out there? Tom Grandy wtg at corral.uwyo.edu --QH7TbvXB6itkIG/XESEDvB==