Re: Plot[] problem (plnr) - help !!!

*To*: mathgroup at smc.vnet.net*Subject*: [mg15964] Re: Plot[] problem (plnr) - help !!!*From*: "Allan Hayes" <hay at haystack.demon.co.uk>*Date*: Fri, 19 Feb 1999 03:26:53 -0500*References*: <7ag3bt$aj1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Alexander Sirotkin wrote in message <7ag3bt$aj1 at smc.vnet.net>... >Hi. > >I'm trying to do most trivial and simple thing - define >some function and then Plot[] it. However, I get some very >weird error - " ...is not a machine-size real number at ..." > >Here is the code : >a[0]==1 >a[1]==0.99/50000 >H[w] == 20Log[10,Sum[a[k] Exp[I 2Pi w(-k)], {k,0,1}]] >Clear[H] >Plot[H[w], {w, 1, 100}] > >I've seen some articles (even at www.wolfram.com) about that >problem, but NONE of them proposed a working solution !!! > >Just putting Evaluate[] inside the Plot[] does nothing... > Alexander Use = or :=, not == in definitions. Use H[w_] == 20Log[10,Sum[a[k] Exp[I 2Pi w(-k)], {k,0,1}]] Don't clear H before you use it. Even so the H gives some complex values which cannot be plotted. Allan --------------------- Allan Hayes Mathematica Training and Consulting Leicester UK www.haystack.demon.co.uk hay at haystack.demon.co.uk Voice: +44 (0)116 271 4198 Fax: +44 (0)870 164 0565