Is there any necessity to pass a variable parameter to a method while the variable declared global?

I am writing a class in java of Monte-Carlo algorithm. Here is the written code -

public class MonteCarlo {
    int[][] matrix;
    public void monteCarlo(List<Node> nodeList) {
        matrix = new int[nodeList.size()][nodeList.size()];
    }

    private void initMatrix(List<Node> list, int[][] matrix) {

    }
}

In here initMatrix method i am passing two parameter. But the matrix array is globally declared. I personally sometime found that is helpful to keep track which method is responsible for what. But is it a bad coding practice to pass a variable parameter even it is declared in globally.