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Annotation of 43BSD/usr.lib/learn/C/L43.1b, revision 1.1

1.1     ! root        1: #print
        !             2: Write a subroutine myexp(x) which expects a floating
        !             3: argument x and returns the floating point value
        !             4: of e to the x.  An adequate algorithm
        !             5: for the purpose is the standard Maclaurin series
        !             6: 
        !             7:    x            2       3       4
        !             8:   e  = 1 + x + x /2! + x /3! + x /4! + ...
        !             9: Name your routine myexp(), not exp().  You can test it, then,
        !            10: by comparing it with the system routine as well as by
        !            11: comparing it with tables.  Leave it on file
        !            12: myexp.c, and then type "ready".
        !            13: #once #create reldif.c
        !            14: double reldif(a,b)
        !            15:  double a,b;
        !            16: {
        !            17: double c,d;
        !            18: if (a==0. && b==0.) return(0.);
        !            19: c = a>0 ? a : -a;
        !            20: d = b>0 ? b : -b;
        !            21: c = c>d ? c : d;
        !            22: return( (a-b)/c );
        !            23: }
        !            24: #once #create tzaqc.c
        !            25: main()
        !            26: {
        !            27: double x,y, log(), myexp(), reldif();
        !            28: for(x=1.; x<5.; x=+ 0.2)
        !            29:   {
        !            30:   y = myexp(x);
        !            31:  if (reldif(x, log(y)) >1.e-5) return(1);
        !            32:   }
        !            33: return(0);
        !            34: }
        !            35: exp()
        !            36: {
        !            37: printf("Cheat! you called the system routine\n");
        !            38: return(1.2);
        !            39: }
        !            40: #user
        !            41: cc tzaqc.c myexp.o reldif.c
        !            42: a.out
        !            43: #succeed
        !            44: /* one way */
        !            45: double myexp(x)
        !            46: double x;
        !            47: {
        !            48:        double term, sum, dabs();
        !            49:        int n;
        !            50:        
        !            51:        term = sum = 1.0;
        !            52:        n = 1;
        !            53:        while (dabs(term) > dabs(sum)/1.e8) {
        !            54:                term = term * x / n++;
        !            55:                sum += term;
        !            56:        }
        !            57:        return(sum);
        !            58: }
        !            59: 
        !            60: double dabs(x)
        !            61: double x;
        !            62: {
        !            63:        return(x>0 ? x : -x);
        !            64: }
        !            65: #log
        !            66: #next
        !            67: 50.1a 10

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