PROGRAM SIMPSON
      PARAMETER( M=10000 )
      REAL X(0:M), Y(0:M)
      REAL DX
      INTEGER L
      REAL XMIN, XMAX
      WRITE(*,*) "INPUT THE STEP NUMBER, XMIN, XMAX"
      READ(*,*) N, XMIN, XMAX
      S=0.0
*-- きざみ幅の設定 ---
      DX=(XMAX-XMIN)/N
*-- 計算ステップの設定 ---
      L=N/2
*-- 開始位置の指定 ---
      X(0)=XMIN
      Y(0)=1.0/(X(0)**2+1.0)
*-- 関数の設定 ---
      DO 20 J=1,N
         X(J)=X(J-1)+DX
         Y(J)=1.0/(X(J)**2+1.0)
  20  CONTINUE
*-- 積分の計算 ---
      DO 10 I=0,L-1
         S=S+(DX/3.0)*(Y(2*I+2)+4.0*Y(2*I+1)+Y(2*I))
  10  CONTINUE
      WRITE(*,*) S
      STOP
      END