ForwSub
Advanced Analysis Library Only
AnalysisLibErrType ForwSub (void *inputMatrixA, double knownVectory[], ssize_t arraySizes, double outputVectorx[], ssize_t permutationVector[]);
Purpose
Solves linear equations AX=Y using forward substitution. ForwSub assumes that A is an LU-decomposed lower triangular matrix. ForwSub obtains X using the following formulas:
x0 = y0
for i = 1, 2, . . ., arraySizes – 1
ForwSub can perform the operation in place; that is, the input and output arrays can be the same.
Example Code
/* to solve a linear equation A*x = y */
double A[10][10], x[10], y[10];
int p[10]; /* permutation vector */
int sign, n;
n = 10;
LU (A, n, p, &sign); /* LU decomposition of A */
ForwSub (A, y, n, x, p); /* forward substitution */
BackSub (A, x, n, x); /* backward substitution */
Parameters
| Input | ||
| Name | Type | Description |
| inputMatrix_A | void * | The lower triangular matrix from LU decomposition. This matrix must be an array of doubles. |
| knownVector_y | double [] | Array that represents the set of known vector coefficients. |
| arraySizes | ssize_t | The number of rows and columns in the square input matrix and the number of elements in the known vector array. |
| permutationVector | ssize_t [] | The permutation vector obtained from the LU decomposition. This vector has the row exchange information. If there was no row exchange in LU, pi = i. |
| Output | ||
| Name | Type | Description |
| outputVector_x | double [] | The solution vector. |
Return Value
| Name | Type | Description |
| status | AnalysisLibErrType | A value that specifies the type of error that occurred. Refer to analysis.h for definitions of these constants. |
Additional Information
Library: Advanced Analysis Library
Include file: analysis.h
LabWindows/CVI compatibility: LabWindows/CVI 3.1 and later