Thread: Sparse matrix and linked list in C

Hi, I need to represent a sparse matrix using liked list in C:
The structure definition is the following;

Code:

typedef struct matrix{
    struct matrix *right;
    struct matrix *below;
    int rowptr, colptr;
    double val;
}Matrix;

I know that right is pointing to the next non-zero element of the row (below points to the non-zero element of the column).
I need to define this functions:

1.- Matrix* initiate(void), which uses stdin to read the non-zero element from a .txt file (which only contains the non-zero values).
2.- void print(Matrix*), it prints the matrix using stdout.
3.- Matrix* add(Matrix*, Matrix*);
4.- void set_elemnt(Matrix* A, int i, int j, double x): assigns A(i,j)=x.
5.- double get_element(Matrix * A, int i, int j); returns A(i,j).
I don't know how to define the header cells (wich contain nothing), the other cells represents the non-zero values.
What I have so far:

Code:

Matrix* initiate(void){
  Matrix*A=malloc(sizeof(*A));

  A->rowptr=rowptr;
  A->colptr=colptr;

  A->right=malloc(rowptr *sizeof(*rowptr->right));
  A->below=malloc(n *sizeof(*n->col));

  return A;
}

For the header (the one containing nothing), I tried to do this, but I have no idea if it is useful:

Code:

Matrix* initiate_1(void){
     Matrix*A=malloc(sizeof(*A));
  A->rowptr=-1;
  A->colptr=-1;
  A->val=nan;
  A->right=A;
  A->below=A;
}

To add matrix:

Code:

Matrix* add(Matrix*,Matrix*){
     int i;
     Matrix*C = initiate();//I don't know what to put here
     for(int i =0;; i++){//don't know what to put in the middle space
                                                         // don't know what to put here
     }
}

Also, I think I can create a matrix with zeros only, but I'm not sure on how I can do that and if it is of any help. I would appreciate if you could help me with this, I barely understand data structures. Thank you!

Consider these structures.

Code:

struct Col {
  double value;
  int colNumber; // which column this is
  struct Col *next;
};
struct Row {
  int rowNumber;  // which row this is
  struct Col *col;  // column values
  struct Row *next;
};

struct Matrix {
  int numRows;  // how big the matrix is
  int numCols;
  struct Row *row; // linked list of rows
};

A number of utility functions would help you.
- check whether a Row exists
- create a Row with a specific row number, and insert it into the matrix row list
- check whether a Col exists within a given Row
- create a Col with a specific column number, and insert it into the Row list.