二维数组如何分配给一维数组？

Question

I am using apache commons-math library to calculate regression parameter. As shown in figure 2nd and 3rd line, a 2d array is assigned to single array. When i use same code,

I am getting error:

"Type mismatch error:cannot convert from double [][] to double []" in 3rd line but not for 2nd line.

OLSMultipleLinearRegression regression = new OLSMultipleLinearRegression();
double[] y = new double[]{11.0, 12.0, 13.0, 14.0, 15.0, 16.0};
double[] x = new double[6][];
x[0] = new double[]{0, 0, 0, 0, 0};
x[1] = new double[]{2.0, 0, 0, 0, 0};
x[2] = new double[]{0, 3.0, 0, 0, 0};
x[3] = new double[]{0, 0, 4.0, 0, 0};
x[4] = new double[]{0, 0, 0, 5.0, 0};
x[5] = new double[]{0, 0, 0, 0, 6.0};          
regression.newSample(y, x);

why this is happening? and how this works?

More details on OLS regression are given here

Answer 1

Case 1 :

   double[] y = new double[]{11.0, 12.0, 13.0, 14.0, 15.0, 16.0};

You are creating a 1D array with values inserting it right away. Works fine

Case 2 :

double[] x = new double[6][];

You are declaring a 1D array and trying to assign a 2D array. Which is illegal.

Either change your declaration to 2D or initialize with 1D

valid declarations will be

double[] x = new double[6];  // 1D

or

double[][] x = new double[6][lenghtYouWant]; //2D

After seeing the insertions later on you are wanting a 2D array. To compile the below code successfully you need to change the delcaration to

double[][] x = new double[6][];