size(580,320);

int numRows = 5;
int numCols = 3;

float jumpX = 1.0 * (width-1) / numCols;
float jumpY = 1.0 * (height-1) / numRows;

stroke(127);
for (int k=0; k <= numCols; k++) {
    line(k*jumpX, 0, k*jumpX, height);
}

for (int k=0; k <= numRows; k++) {
    line(0, k*jumpY, width, k*jumpY);
}

save("solidGrid2.png");