Re: HELP : Mathematica v4 producing erroneous results ! Mathematica3 worked fine...

*To*: mathgroup at smc.vnet.net*Subject*: [mg19039] Re: [mg18954] HELP : Mathematica v4 producing erroneous results ! Mathematica3 worked fine...*From*: "Tomas Garza" <tgarza at mail.internet.com.mx>*Date*: Tue, 3 Aug 1999 13:45:07 -0400*Sender*: owner-wri-mathgroup at wolfram.com

Chris Slinger [slinger at signal.dra.hmg.gb] wrote: > We recently upgraded to Mathematica v4 on NT and Solaris from > Mathematica v3. > To my horror, I discovered that notebooks which produced good > results under 3 produced > errroneous ones under v4. > > I have traced the fault, and the code below is distilled down to > illustrate the > problem. Basically, I'm simply assigning complex numbers to an > array using a > Do[] (but note the Fourier[], which seems to be necessary to > cause the bug, for > some reason). Unfortunately, the imaginary parts of the result > are not correct > - their values should be as in the array "ideal" but are simply > equal to the > real parts !! > > Can people reproduce it ? What is going on ? No comments please > on style or > content - remember this is a cut down version of a far larger > notebook just to > illustrate the point: > > In[1]:= $Version > Out[1]= "4.0 for Microsoft Windows (April 21, 1999)" > > In[2]:= SeedRandom[1]; > ideal=Table[Random[Complex,{-1-I,+1+I}],{2},{2}] > > Out[2]= {{0.337385+0.6624 I], 0.563615-0.750732 > I},{0.869075+0.200504 I, > 0.516709+0.938178 I}} > > In[3]:= output=Fourier[ideal]; > Do[output[[i,j]]=ideal[[i,j]],{i,1,2},{j,1,2}]; > output > > Out[3]= {{0.337385+0.337385 I, 0.563615+0.563615 I},{0.869075+0.869075 I, > 0.516709+0.516709 I}} > > Why does Out[3] not equal Out[2] ? In Mathematica v3, there is > no problem. > > The upshot of this is that we have "downgraded" back to > Mathematica v3 until this is > sorted out (the fragment of code above is distilled from our > computer generated > holography design algorithms). > > I've asked Wolfram Support to help out, but am awaiting their comments. Chris, Indeed, t'is strange! I checked your results both in Versions 3 and 4 (under Windows 98), and I obtain the same as you. The funny thing is, Trace[] gives identical output in both cases. This looks as if it's a real bug. I hope Wolfram Support will take a close look at it. Tomas Garza Mexico City