Abs[] help please

*To*: mathgroup at smc.vnet.net*Subject*: [mg5399] Abs[] help please*From*: robpeterson at sprintmail.com (Rob Peterson)*Date*: Thu, 5 Dec 1996 14:50:33 -0500*Organization*: Sprint Internet Passport*Sender*: owner-wri-mathgroup at wolfram.com

I may not understand the limitations of Abs[]. This works just fine: s[L_]=I/(L+1/L);(* a complex function *) Plot[Evaluate[D[Abs[s[L]],L]],{L,1,2}] (*The Abs[] of a complex function, which is real, apparently has a real derivative and it is plotted.*) However, If I put another "I" in the function definition, the derivative of the Abs[] appears to have an imaginary component: s[L_]=I/(L+I/L);(* has I instead of 1 *) Plot[Evaluate[D[Abs[s[L]],L]],{L,1,2}] The error message is as follows Plot::"plnr": (1 - I/L^2)* REAL "is not a mach. size real number". For some reason a factor of (1-I/L^2) showed up (REAL is some real function). Can anyone give me a clue how I might be able to plot the derivative of the Abs[] of this type of complex function?