Abelian sandpile model: Difference between revisions

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 0 0  0  0    0 2 1 2 0
 0 0  0  0    0 0 1 0 0
+</pre>
+=={{header|C}}==
+Writes out the initial and final sand piles to the console and the final sand pile to a PPM file.
+<lang C>
+#include<stdlib.h>
+#include<string.h>
+#include<stdio.h>
+int main(int argc, char** argv)
+{
+	int i,j,sandPileEdge, centerPileHeight, processAgain = 1,top,down,left,right;
+	int** sandPile;
+	char* fileName;
+	static unsigned char colour[3];
+	if(argc!=3){
+		printf("Usage: %s <Sand pile side> <Center pile height>",argv[0]);
+		return 0;
+	}
+	sandPileEdge = atoi(argv[1]);
+	centerPileHeight = atoi(argv[2]);
+	if(sandPileEdge<=0 || centerPileHeight<=0){
+		printf("Sand pile and center pile dimensions must be positive integers.");
+		return 0;
+	}
+	sandPile = (int**)malloc(sandPileEdge * sizeof(int*));
+	for(i=0;i<sandPileEdge;i++){
+		sandPile[i] = (int*)calloc(sandPileEdge,sizeof(int));
+	}
+	sandPile[sandPileEdge/2][sandPileEdge/2] = centerPileHeight;
+	printf("Initial sand pile :\n\n");
+	for(i=0;i<sandPileEdge;i++){
+		for(j=0;j<sandPileEdge;j++){
+			printf("%3d",sandPile[i][j]);
+		}
+		printf("\n");
+	}
+	while(processAgain == 1){
+		processAgain = 0;
+		top = 0;
+		down = 0;
+		left = 0;
+		right = 0;
+		for(i=0;i<sandPileEdge;i++){
+			for(j=0;j<sandPileEdge;j++){
+				if(sandPile[i][j]>=4){
+					if(i-1>=0){
+						top = 1;
+						sandPile[i-1][j]+=1;
+						if(sandPile[i-1][j]>=4)
+							processAgain = 1;
+					}
+					if(i+1<sandPileEdge){
+						down = 1;
+						sandPile[i+1][j]+=1;
+						if(sandPile[i+1][j]>=4)
+							processAgain = 1;
+					}
+					if(j-1>=0){
+						left = 1;
+						sandPile[i][j-1]+=1;
+						if(sandPile[i][j-1]>=4)
+							processAgain = 1;
+					}
+					if(j+1<sandPileEdge){
+						right = 1;
+						sandPile[i][j+1]+=1;
+						if(sandPile[i][j+1]>=4)
+							processAgain = 1;
+					}
+				sandPile[i][j] -= (top + down + left + right);
+				if(sandPile[i][j]>=4)
+					processAgain = 1;
+				}
+			}
+		}
+	}
+	printf("Final sand pile : \n\n");
+	for(i=0;i<sandPileEdge;i++){
+		for(j=0;j<sandPileEdge;j++){
+			printf("%3d",sandPile[i][j]);
+		}
+		printf("\n");
+	}
+	fileName = (char*)malloc((strlen(argv[1]) + strlen(argv[2]) + 23)*sizeof(char));
+	strcpy(fileName,"Final_Sand_Pile_");
+	strcat(fileName,argv[1]);
+	strcat(fileName,"_");
+	strcat(fileName,argv[2]);
+	strcat(fileName,".ppm");
+	FILE *fp = fopen(fileName,"wb");
+	fprintf(fp,"P6\n%d %d\n255\n",sandPileEdge,sandPileEdge);
+	for(i=0;i<sandPileEdge;i++){
+		for(j=0;j<sandPileEdge;j++){
+			colour[0] = (sandPile[i][j] + i)%256;
+			colour[1] = (sandPile[i][j] + j)%256;
+			colour[2] = (sandPile[i][j] + i*j)%256;
+			fwrite(colour,1,3,fp);
+		}
+	}
+	fclose(fp);
+	printf("\nImage file written to %s\n",fileName);
+	return 0;
+}
+</lang>
+Console output :
+<pre>
+abhishek_ghosh@Azure:~/doodles$ ./a.out 10 64
+Initial sand pile :
+0  0  0  0  0  0  0  0  0
+0  0  0  0  0  0  0  0  0
+0  0  0  0  0  0  0  0  0
+0  0  0  0  0  0  0  0  0
+0  0  0  0  0  0  0  0  0
+0  0  0  0 64  0  0  0  0
+0  0  0  0  0  0  0  0  0
+0  0  0  0  0  0  0  0  0
+0  0  0  0  0  0  0  0  0
+0  0  0  0  0  0  0  0  0
+Final sand pile :
+0  0  0  0  0  0  0  0  0
+0  0  0  0  0  0  0  0  0
+0  0  0  1  2  1  0  0  0
+0  0  2  2  2  2  2  0  0
+0  1  2  2  2  2  2  1  0
+0  2  2  2  0  2  2  2  0
+0  1  2  2  2  2  2  1  0
+0  0  2  2  2  2  2  0  0
+0  0  0  1  2  1  0  0  0
+0  0  0  0  0  0  0  0  0
+Image file written to Final_Sand_Pile_10_64.ppm
 </pre>