C languange DGEQRF 示例，link liblapack.a

1.示例源码

#include <stdio.h>

int min(int m, int n){  return m<n? m:n;}


void print_matrix(double* A, int m, int n, int lda)
{
        for (int i = 0; i < m; i++)
        {
                for (int j = 0; j < n; j++)
                {
                        //printf("%7.4f ", A[i + j*lda]);
                        printf("%7.4f, ", A[i + j * lda]);
                }
                printf("; ...\n");
        }
}


int main()
{
    int m = 4; // Number of rows in the matrix
    int n = 4; // Number of columns in the matrix
    //double A[] = {1.0, 4.0, 2.0, 5.0, 3.0, 6.0}; // Input matrix
    //double A[] = { 0.2029,  0.1386,  0.0747,  0.4070,  0.3765,  0.9046,  0.5039,  0.1746,  0.1999,  0.1830,  0.0428,  0.5782,  0.4996,  0.0351,  0.3829,  0.4178,  0.7555,  0.8836,  0.1705,  0.5099,  0.7483,  0.1933,  0.0904,  0.0653,  0.5536,  0.1145,  0.0588,  0.7315,  0.5379,  0.1212,  0.4357,  0.5835,  0.5118,  0.1740,  0.6601,  0.8425,  0.6992,  0.4402,  0.2148,  0.6044,  0.6756,  0.1013,  0.3293,  0.3598,  0.9349,  0.2801,  0.3233,  0.5857,  0.2380}; // Input matrix
    double A[] = {
                        0.2029,  0.1386,  0.0747,  0.4070,
                        0.3765,  0.9046,  0.5039,  0.1746,
                        0.1999,  0.1830,  0.0428,  0.5782,
                        0.4996,  0.0351,  0.3829,  0.4178
                }; // Input matrix
        printf("A =\n");
        print_matrix(A, m, n, m);
    int lda = m; // Leading dimension of A
    double tau[min(m,n)]; // Array to store elementary reflectors
    int info; // Output variable for error info

    int lwork = -1;
    double* work = (double*)malloc(8);
    // Call the LAPACK dgeqrf function for QR decomposition
    dgeqrf_(&m, &n, A, &lda, tau, work, &lwork, &info);

    lwork = (int)work[0];
    printf("lwork=%d\n", lwork);
    work = (double*)malloc(lwork*sizeof(double)); // Workspace array

    // Call the LAPACK dgeqrf function again with correct workspace
    dgeqrf_(&m, &n, A, &lda, tau, work, &lwork, &info);

    if (info == 0) {
        printf("QR decomposition successful!\n");
        // Print the decomposed matrix A
        printf("Decomposed matrix A:\n");
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                printf("%8.5f ", A[i + j*m]);
            }
            printf("\n");
        }
    } else {
        printf("QR decomposition failed!\n");
    }

printf("\nTAU=\n");
for(int i=0; i<min(m,n); i++)
{
        printf(" %8.5f ", tau[i]);
}
printf("\n\n");
    return 0;
}

2. Makefile

STATIC_LIB =  ../../liblapack.a ../../librefblas.a
LD_FLAGS   =  -lgfortran  -lm

EXE := dgeqrf_

all: $(EXE)

%: %.c
        gcc -g $< $(STATIC_LIB) $(LD_FLAGS) -o $@


.PHONY: clean
clean:
        ${RM} $(EXE) *.o

3. 运行