Created
February 10, 2022 19:27
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Find Determinant
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REAL(dp) FUNCTION FindDet(matrix, n) | |
IMPLICIT NONE | |
REAL(dp), DIMENSION(n,n) :: matrix | |
INTEGER, INTENT(IN) :: n | |
REAL :: m, temp | |
INTEGER :: i, j, k, l | |
LOGICAL :: DetExists = .TRUE. | |
l = 1 | |
!Convert to upper triangular form | |
DO k = 1, n-1 | |
IF (matrix(k,k) == 0) THEN | |
DetExists = .FALSE. | |
DO i = k+1, n | |
IF (matrix(i,k) /= 0) THEN | |
DO j = 1, n | |
temp = matrix(i,j) | |
matrix(i,j)= matrix(k,j) | |
matrix(k,j) = temp | |
END DO | |
DetExists = .TRUE. | |
l=-l | |
EXIT | |
ENDIF | |
END DO | |
IF (DetExists .EQV. .FALSE.) THEN | |
FindDet = 0 | |
return | |
END IF | |
ENDIF | |
DO j = k+1, n | |
m = matrix(j,k)/matrix(k,k) | |
DO i = k+1, n | |
matrix(j,i) = matrix(j,i) - m*matrix(k,i) | |
END DO | |
END DO | |
END DO | |
!Calculate determinant by finding product of diagonal elements | |
FindDet = l | |
DO i = 1, n | |
FindDet = FindDet * matrix(i,i) | |
END DO | |
END FUNCTION FindDet |
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