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why 312/100 and 3.12 different

  • To: mathgroup at
  • Subject: [mg7988] why 312/100 and 3.12 different
  • From: "H.J. Wang" <hungjen at>
  • Date: Wed, 30 Jul 1997 23:57:39 -0400
  • Organization: University of Michigan
  • Sender: owner-wri-mathgroup at


        I observed a very strange behavior of Mma 2.2.3 when trying to
evaluate the following program in Win95.

(******** begin of the program ***********)
ldist =LogNormalDistribution[m,s];
logpdf[W_] = PDF[ldist, W];
pa =CDF[ldist, e];
pc = 1-CDF[ldist, wtilde];
pb = CDF[ldist, wtilde] - CDF[ldist, e];
wtilde = (e+b (1+r))/(1+c);
U[X_,L_] = Log[X] +0.0003*L^11;
Y2=312/100 n2;
Y1=312/100 n1;
Ux[X_,L_] = D[U[X,L],X];

funEU = U[w+Y1+b,n1] +
 rho Integrate[ U[ W (1-c)+ei Y2,n2]*logpdf[W], {W,0,e}]+ rho
 Integrate[ U[ e-c W+ei Y2,n2] logpdf[W], {W,e,wtilde}] + rho
 Integrate[ U[ W+Y2-b (1+r),n2] logpdf[W], {W,wtilde,Infinity}];

(****** end of the program ****************)

        The strange thing is observed when I change the 9th and the
10th lines from
        Y2 = 312/100 n2;
        Y1 = 312/100 n1;
        Y2 = 3.12 n2;
        Y1 = 3.12 n1;

.  With the "312/100" coefficients, the execution time is short and the
memory usage is (relatively) minimal.  However, with the "3.12"
coefficients, Mma used up all the RAM (about 25 MB available for it)
and has to resort to virtual memory.  I don't know whether it will
eventually produce results since I interrupted the process.

        Any idea of why this might happen and how could we avoid it?
Thank you in advance!

H.J. Wang

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