re: eval differential expressions
- To: mathgroup at yoda.physics.unc.edu
- Subject: re: eval differential expressions
- From: "Dr A. Hayes" <hay at leicester.ac.uk>
- Date: Mon, 20 Jun 1994 15:41:24 +0100 (BST)
Geoff Latham <gal at melba.bby.com.au writes: > Is there an easy way to evaluate differential expressions for various > functions? > For example, if I have D[f[x],x]^2+f[x] in Mma, I'd like to evaluate it for > various functions f[x]. This can be done via naming the expression and > then letting f[x_]=<desired fn of x> and typing the expressions name > upon which its evaluated - but this seems awfully clumbsy! > Any suggestions? > Thanks. Here are two ways: In[1]:= op[exp_,v_:x] := D[exp,v]^2+exp (*The v_:x makes x the default independent variable.*) In[2]:= op[Sin[x]] Out[2] = Cos[x]^2 + Sin[x] In[3]:= op[Sin[t],t] Out[3]= Cos[t]^2 + Sin[t] And a functional variant In[4]:= opf[f_] := (f'[#]^2 + f[#])& In[5]:= opf[Sin][x] Out[5]= Cos[x]^2 + Sin[x] Allan Hayes, hay at le.ac.uk