fortran77 to matlab convert

Question

msh 2014-7-25

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/143310-fortran77-to-matlab-convert

评论： msh 2014-7-25

Hi,

i would like to convert this code of F77 to matlab. I am confused on one particular step, the "goto" and more specifically I cannot understand whether there is any update on the loop or not.

Here it is the code

      subroutine qgausl(n,x1,x2,x,w)
      implicit double precision (a-h,o-z)
      double precision x(n),w(n),x1,x2
      eps=1.0e-8
      m=(n+1)/2
      xm=0.5*(x2+x1)
      xl=0.5*(x2-x1)
      do 12 i=1,m
        z = cos(3.141592654*(i-.25)/(n+.5))
1       continue
          p1 = 1.0
          p2 = 0.0
          do 11 j=1,n
            p3 = p2
            p2 = p1
            p1 = ((2.0*j-1.0)*z*p2-(j-1.0)*p3)/j
 11       continue
          pp = n*(z*p1-p2)/(z*z-1.0)
          z1 = z
          z = z1-p1/pp
          if (dabs(z-z1).gt.eps) go to 1
          x(i) = xm-xl*z
          x(n+1-i) = xm+xl*z
          w(i) = 2.0*xl/((1.0-z*z)*pp*pp)
          w(n+1-i) = w(i)
 12   continue
      return
      end

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Answer 1

David Young 2014-7-25

1
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https://ww2.mathworks.cn/matlabcentral/answers/143310-fortran77-to-matlab-convert#answer_146391

在 MATLAB Online 中打开

The code from "1 continue" to "go to 1" could be translated into a while loop, something like

z1 = z + 1;    % initial value so loop will be executed once
while abs(z-z1) > eps
   < ... code ... >
end

You have three nested loops. All of them have updates of variables or arrays inside them. The "go to" loop updates z and z1, and their difference is presumably expected to converge towards zero.