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      program problem_1
c This program will calculate y=sin(x) and write out (x,y) to
c screen and to a file.
      real y(100), x(100), delta_x
      integer i
      delta_x = 4.0*3.14159/100.0
      open(unit=10, file='sin.dat')
      do i=1, 100
        x(i) = (i-1)*delta_x
        y(i) = sin(x(i))
        write(*,*) x(i), y(i)
        write(10,*) x(i), y(i)
      end do
      close(10)
      end