spvar.f

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C> @file
C> @brief Compute variance by total wavenumber.
C> @author Iredell @date 92-10-31
 
C> Computes the variances by total wavenumber
C> of a scalar field in spectral space.
C>
C> @param I spectral domain shape
C> (0 for triangular, 1 for rhomboidal)
C> @param M spectral truncation
C> @param Q ((M+1)*((I+1)*M+2)) scalar field
C> @param QVAR (0:(I+1)*M) variances
C>
C> @author Iredell @date 92-10-31
      SUBROUTINE spvar(I,M,Q,QVAR)
      REAL Q((M+1)*((I+1)*M+2))
      REAL QVAR(0:(I+1)*M)
 
      l=0
      DO n=0,m
        ks=l*(2*m+(i-1)*(l-1))+2*n
        qvar(n)=0.5*q(ks+1)**2
      ENDDO
      DO n=m+1,(i+1)*m
        qvar(n)=0.
      ENDDO
      DO n=0,(i+1)*m
        DO l=max(1,n-m),min(n,m)
          ks=l*(2*m+(i-1)*(l-1))+2*n
          qvar(n)=qvar(n)+q(ks+1)**2+q(ks+2)**2
        ENDDO
      ENDDO
 
      RETURN
      END