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Re: Very simple question

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From	Alexei Boulbitch <Alexei.Boulbitch@iee.lu>
Newsgroups	comp.soft-sys.math.mathematica
Subject	Re: Very simple question
Date	Fri, 11 Apr 2014 06:11:18 +0000 (UTC)
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I've been away from Mathematica for about 7 years.
Can anyone tell me why function fx gives an error message but fy does
not? They look functionally the same to me.
Please send me an email about this.

fx[ptl_] := Module[{x1, y1, x2, y2, x3, y3},
   Print[pt1];
   x1 = pt1[[1, 1]]; y1 = pt1[[1, 2]];
   x2 = pt2[[2, 1]]; y2 = pt2[[2, 2]];
   x3 = pt3[[3, 1]]; y3 = pt3[[3, 2]];
   Print[x1, y1, x2, y2, x3, y3];
   ]
fx[{{1, 2}, {3, 5}, {4, 7}}]

fy[pt1_] := Module[{zz, x1, y1, x2, y2, x3, y3},
   zz = pt1;
   Print[zz];
   x1 = zz[[1, 1]]; y1 = zz[[1, 2]];
   x2 = zz[[2, 1]]; y2 = zz[[2, 2]];
   x3 = zz[[3, 1]]; y3 = zz[[3, 2]];
   Print[x1, y1, x2, y2, x3, y3]
   ]
fy[{{1, 2}, {3, 5}, {4, 7}}]

Thank you.
Steve Gray
stevebg at roadrunner.com




Hi, Stephen,

The answer is also simple: the body of the function fx calls pt2 and pt3 that are not defined anywhere. It confuses Mathematica. If you replace fx as follows:

fx[pt1_] := Module[{x1, y1, x2, y2, x3, y3},
 
  x1 = pt1[[1, 1]];
  y1 = pt1[[1, 2]];
  x2 = pt1[[2, 1]];
  y2 = pt1[[2, 2]];
  x3 = pt1[[3, 1]];
  y3 = pt1[[3, 2]];
  Print[x1, y1, x2, y2, x3, y3]]

Which is probably what you intended, it will return the result. In messages though. To see the result on the screen it is better to do something like the following:

fz[pt1_] := Module[{x1, y1, x2, y2, x3, y3},
 
  x1 = pt1[[1, 1]];
  y1 = pt1[[1, 2]];
  x2 = pt1[[2, 1]];
  y2 = pt1[[2, 2]];
  x3 = pt1[[3, 1]];
  y3 = pt1[[3, 2]];
  {x1, y1, x2, y2, x3, y3}]


fz[{{1, 2}, {3, 5}, {4, 7}}]

{1, 2, 3, 5, 4, 7}

Have fun, Alexei


Alexei BOULBITCH, Dr., habil.
IEE S.A.
ZAE Weiergewan,
11, rue Edmond Reuter,
L-5326 Contern, LUXEMBOURG

Office phone :  +352-2454-2566
Office fax:       +352-2454-3566
mobile phone:  +49 151 52 40 66 44

e-mail: alexei.boulbitch@iee.lu

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Re: Very simple question Alexei Boulbitch <Alexei.Boulbitch@iee.lu> - 2014-04-11 06:11 +0000

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