Segmentation error

nhanlm0601 (8)
I have a problem of this C++ program when trying to execute
it says "Segmentation Error"
and did not give which line I need to fix, so... generally, I am doomed, and I need help...

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/*******************LINEAR CHAIN**********************
|    this program is developed to calculate the eigenvalues and 	|
| eigenvectors of a linear chain of n-masses and (n+1)springs		|
| where n is even. Using Jacobian's method for sym. matrix		|
|		The chain is limited up to diatomic chain	|
******************************************************/


#include <iostream>
using namespace std;
#include <math.h>
//stdlib for memory allocation/ dynamic memory
#include <stdlib.h>

void matrix_alloc( double **array, int nrows, int ncolumns);
void matrix_init( double **array, int n);
void matrix_init_identity( double **array, int n);
void update( int k, double t, double& y, double e[], bool changed[], int& state);
/*void update(index k, parameter t, parameter y, eigenvector e[], changed[], state*/
void rotate(int k, int l, int i, int j, double **matrix, double c, double s);
int maxind (int k, double **array, int n);

int main(){
	int n=10;			// n need to be even to create continous boundary
	double **E, **S;
	//dynamic memory allocation to E[][] and S[][]
	matrix_alloc(E, n, n);
	matrix_alloc(S, n, n);
	//varible declaration
	double e[n];
	int i, k, l, m, state;
	double s, c, t, p, y;
	int ind[n];
	bool changed[n];
	//manually set the spring constant nad mass
	double spring[2] = {10, 10};
	double mass [2] = {1, 1};

	//Assign components to matrix S[][] only works for even nxn matrix
	for ( i = 0; i < (n-2); i = i+2){ //set for upper, lower diagonal and diagonal
		S[i][i+1] = -spring[1]/mass[0];
		S[i+1][i] = -spring[1]/mass[1];
		S[i][i] = (spring[0] + spring[1]) / mass[0];
	};
	for ( i = 1; i < (n-3); i = i+2){
		S[i][i+1] = -spring[0]/mass[1];
		S[i+1][i] = -spring[0] / mass[0];
		S[i][i] = (spring[0] + spring[1]) / mass[1];
	};
	S[n-1][n-1] = (spring[0] + spring[1]) / mass[1];
	S[0][n-1] = -spring[0] / mass[0];
	S[n-1][0] = -spring[0] / mass[1];
	
	//init E[][] and arrays ind[], e[], changed[]
	matrix_init_identity( E, n);
	state = n;
	for (k=0; k<n; k++){
		ind[k] = maxind( k, S, n);
		e[k] = S[k][k];
		changed[k] = true;
	};
	//rotation around biggest index - pivot p(k,l)- by Givens' matrix
	while ( state != 0) {
		m = 0;
		//find pivot p( k, l)
		for ( k=1; k < (n-1); k++){
			if ( fabs( S[k][ind[k]]) > fabs(S[m][ind[m]]))
				m = k;
		};
		//prepare Givens' matrix's components
		k = m;
		l = ind[m];
		p = S[k][l];
		y = (e[l] - e[k])/2;		t = fabs(y) + sqrt( p*p + y*y );
		s = sqrt( p*p + t*t);		
		c = t/s;
		s = p/s;
		t = p*p/t;
		if (y<0){
			s = -s;
			t = -t;
		};
		S[k][l] = 0;
		update( k, -t, y, e, changed, state);
		update( l, t, y, e, changed, state);
		//rotate rows and columns k, l
		for ( i = 0; i < k; i++) rotate(i, k, i, l, S, c, s);
		for ( i = k + 1; i < l; i++) rotate( k, i, i, l, S, c, s);
		for ( i = l + 1; i < n; i++) rotate( k, i, l, i, S, c, s);
		//rotate eigenvectors
		for ( i = 0; i < n; i++) rotate ( k, i, l, i, E, c, s);
		// update rows k, l by changing ind[k], ind[l]
		ind[k] = maxind( k, S, n);
		ind[l] = maxind(l, S, n);
	};
};

//***************Function*******************
void matrix_alloc (double **array, int nrows, int ncolumns){
	if (array != 0){
		cout << "error allocating memory"<<endl;
		return;
	};
	array = (double**)malloc(nrows * sizeof(int *));
	if(array == NULL){
		cout << "error allocating memory"<<endl;
		return;
		};
	for(int i = 0; i < nrows; i++){
		array[i] = (double*)malloc(ncolumns * sizeof(int));
		if ( array[i] == NULL){
			cout << "error allocating memory"<<endl;
			return;
		};
	};
};
void matrix_init( double **array, int n){
	for (int i=0; i < n; i++){
		for (int j=0; j < n; j++) {
			array[i][j] = 0;
		};
	     };
};
void matrix_init_identity (double **array, int n){
	for (int i=0; i < n; i++){
		for (int j=0; j < n; j++) {
			if (i == j){
				array[i][j] = 1;
			}else{
				array[i][j] = 0;
			};
		};
	     };
};
void update( int k, double t, double& y, double e[], bool changed[], int& state){
	y = e[k];
	e[k] = y + t;
	if (changed[k] && (y = e[k])){
		changed[k] = false;
		state = state - 1;
	}else{
		if ((!changed[k]) && (y != e[k])){
			changed[k] = true;
			state = state + 1;
		};
	};
};
void rotate(int k, int l, int i, int j, double **matrix, double c, double s){
	double a, b;
	a = c*matrix[k][l] - s*matrix[i][j];
	b = s*matrix[k][l] + c*matrix[i][j];
	matrix[k][l] = a;
	matrix[i][j] = b;
};
int maxind (int k, double **array, int n){ 
	/*find maximum component, off diagonal in (row k) of matrix (array) size (n)*/
	int m = k+1;
	for (int i = k+2; i < n; i++){
		if ( fabs(array[k][i]) > fabs( array[k][m]))
			m = i;
	};
};
Disch (13742)
Your matrix_alloc function does not allocate memory for the pointer passed to it. Instead, it just allocates memory to a local buffer, leaving whatever you called it with unchanged.

Basically, it does nothing but leak memory

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double **E, **S;

matrix_alloc(E, n, n);  // this doesn't change E
matrix_alloc(S, n, n);  // this doesn't change S


If you want matrix_alloc to change E,S ... you'll need to pass them by pointer (which means your function would need to take a double***, or have them returned by the function (so the function returns double** instead of void.

The latter is simpler:

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E = matrix_alloc(n,n);
S = matrix_alloc(n,n);
nhanlm0601 (8)
So, correct me if I am wrong, if I were to do the latter (returned by the function double**)
Is this the right way to do?
it says
error: a function-definition is not allowed here before ‘{’ token


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//***************Function*******************
double** matrix_alloc  ( int nrows, int ncolumns){  //error: a function-definition is not allowed here before ‘{’ token
	double **array;

	array = (double**)malloc(nrows * sizeof(int *));
	if(array == NULL){
		cout << "error allocating memory"<<endl;
		};
	for(int i = 0; i < nrows; i++){
		array[i] = (double*)malloc(ncolumns * sizeof(int));
		if ( array[i] == NULL){
			cout << "error allocating memory"<<endl;
		};
	};
	return array;
};




========================================================
reference

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 /*******************LINEAR CHAIN**********************
 |    this program is developed to calculate the eigenvalues and 		|
 | eigenvectors of a linear chain of n-masses and (n+1)springs		|
 | where n is even. Using Jacobian's method for sym. matrix			|
 |		The chain is limited up to diatomic chain									|
******************************************************/


#include <iostream>
using namespace std;
#include <math.h>
//stdlib for memory allocation/ dynamic memory
#include <stdlib.h>

double** matrix_alloc(int nrows, int ncolumns);
void matrix_init( double **array, int n);
void matrix_init_identity( double **array, int n);
void update( int k, double t, double& y, double e[], bool changed[], int& state);
/*void update(index k, parameter t, parameter y, eigenvector e[], changed[], state*/
void rotate(int k, int l, int i, int j, double **matrix, double c, double s);
int maxind (int k, double **array, int n);

int main(){
	int n=10;			// n need to be even to create continous boundary
	double **E, **S;
	//dynamic memory allocation to E[][] and S[][]
	E = matrix_alloc( n, n);
	S = matrix_alloc( n, n);
	//varible declaration
	double e[n];
	int i, k, l, m, state;
	double s, c, t, p, y;
	int ind[n];
	bool changed[n];
	//manually set the spring constant nad mass
	double spring[2] = {10, 10};
	double mass [2] = {1, 1};

	//Assign components to matrix S[][] only works for even nxn matrix
	for ( i = 0; i < (n-2); i = i+2){ //set for upper, lower diagonal and diagonal
		S[i][i+1] = -spring[1]/mass[0];
		S[i+1][i] = -spring[1]/mass[1];
		S[i][i] = (spring[0] + spring[1]) / mass[0];
	};
	for ( i = 1; i < (n-3); i = i+2){
		S[i][i+1] = -spring[0]/mass[1];
		S[i+1][i] = -spring[0] / mass[0];
		S[i][i] = (spring[0] + spring[1]) / mass[1];
	};
	S[n-1][n-1] = (spring[0] + spring[1]) / mass[1];

	
	//init E[][] and arrays ind[], e[], changed[]
	matrix_init_identity( E, n);
	state = n;
	for (k=0; k<n; k++){
		ind[k] = maxind( k, S, n);
		e[k] = S[k][k];
		changed[k] = true;
	};
	//rotation around biggest index - pivot p(k,l)- by Givens' matrix
	while ( state != 0) {
		m = 0;
		//find pivot p( k, l)
		for ( k=1; k < (n-1); k++){
			if ( fabs( S[k][ind[k]]) > fabs(S[m][ind[m]]))
				m = k;
		};
		//prepare Givens' matrix's components
		k = m;
		l = ind[m];
		p = S[k][l];
		y = (e[l] - e[k])/2;		t = fabs(y) + sqrt( p*p + y*y );
		s = sqrt( p*p + t*t);		
		c = t/s;
		s = p/s;
		t = p*p/t;
		if (y<0){
			s = -s;
			t = -t;
		};
		S[k][l] = 0;
		update( k, -t, y, e, changed, state);
		update( l, t, y, e, changed, state);
		//rotate rows and columns k, l
		for ( i = 0; i < k; i++) rotate(i, k, i, l, S, c, s);
		for ( i = k + 1; i < l; i++) rotate( k, i, i, l, S, c, s);
		for ( i = l + 1; i < n; i++) rotate( k, i, l, i, S, c, s);
		//rotate eigenvectors
		for ( i = 0; i < n; i++) rotate ( k, i, l, i, E, c, s);
		// update rows k, l by changing ind[k], ind[l]
		ind[k] = maxind( k, S, n);
		ind[l] = maxind(l, S, n);
	};
	//cout << data on screen
	for (i = 0; i < n; i++){
		cout << "Eigenvalues are" ;
		cout << e[i] <<endl;
		cout <<"Correspond eigenvectors are " <<endl;
		for (int j = 0; j < n; j++){
			cout<<"     "<< E[i][j];
		};
		cout << endl;		
};

//***************Function*******************
double** matrix_alloc ( int nrows, int ncolumns){
	double **array;

	array = (double**)malloc(nrows * sizeof(int *));
	if(array == NULL){
		cout << "error allocating memory"<<endl;
		};
	for(int i = 0; i < nrows; i++){
		array[i] = (double*)malloc(ncolumns * sizeof(int));
		if ( array[i] == NULL){
			cout << "error allocating memory"<<endl;
		};
	};
	return array;
};
void matrix_init( double **array, int n){
	for (int i=0; i < n; i++){
		for (int j=0; j < n; j++) {
			array[i][j] = 0;
		};
	     };
};
void matrix_init_identity (double **array, int n){
	for (int i=0; i < n; i++){
		for (int j=0; j < n; j++) {
			if (i == j){
				array[i][j] = 1;
			}else{
				array[i][j] = 0;
			};
		};
	     };
};
void update( int k, double t, double& y, double e[], bool changed[], int& state){
	y = e[k];
	e[k] = y + t;
	if (changed[k] && (y = e[k])){
		changed[k] = false;
		state = state - 1;
	}else{
		if ((!changed[k]) && (y != e[k])){
			changed[k] = true;
			state = state + 1;
		};
	};
};
void rotate(int k, int l, int i, int j, double **matrix, double c, double s){
	double a, b;
	a = c*matrix[k][l] - s*matrix[i][j];
	b = s*matrix[k][l] + c*matrix[i][j];
	matrix[k][l] = a;
	matrix[i][j] = b;
};
int maxind (int k, double **array, int n){ 
	/*find maximum component, off diagonal in (row k) of matrix (array) size (n)*/
	int m = k+1;
	for (int i = k+2; i < n; i++){
		if ( fabs(array[k][i]) > fabs( array[k][m]))
		{m = i;}
	};
};

Last edited on
Disch (13742)
Yes you're doing it correctly.

The problem is you are missing a } in main. Count your braces.
nhanlm0601 (8)
thank you Disch,
I am grateful for your help

regards,
N.Le
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