You would need to copy the array elements indivually e.g.

for(int i = 0; i < Gait1.length; i++){
      for(int j = 0; j < Gait1[i].length; j++){
            Gait1[i][j] = GaitFWD[i][j];
      }
}

This assumes that the array Gait1 has been created (using new keyword) and that it is the same size as the GaitFWD array.

I works for me.
Tested with:

1. int  GaitSTOP[][] = {
2.         { 5, 10, 15, 20, 25, 200}
3.       }; 
4.  
5. int GaitFWD[][] = {
6.         { 2, 4, 6, 8, 10, 12, 14, 200 },
7.         { 3, 6, 9, 12, 15, 18, 24, 200 },
8.         { 5, 7, 11, 13, 17, 19, 200 }
9.       };
10.  
11. int Gait1[][] = GaitFWD;
12.  
13. size(800, 300);
14. fill(0);
15. for (int i = 0; i < Gait1.length; i++)
16. {
17.   for (int j = 0; j < Gait1[i].length; j++)
18.   {
19.     ellipse(50 + Gait1[i][j] * 4, 50 + i * 50, 10, 10);
20.   }
21. }

I used arbitrary values for testing purpose.
Replace int Gait1[][] = GaitFWD; with int Gait1[][] = GaitSTOP; and see the difference.
I used arbitrary values for testing purpose.
Note: we usually write arrays in the Java style rather than in the C style:
int [][] GaitFWD = { ... };
int [][] Gait1 = GaitFWD;

Hi,

- int Gait1[][]=GaitFWD; works during the initialization of the array. If I use it later in the code, it doesn't do anything.

This works because you are declaring a 2D array called Gait1 ( int Gait1[][]) and initialising it to another 2D array ( =GaitFWD) To do this after initialisation use

Gait1 = GaitFWD;

In your code (I have copied it below) you have created two arrays called GaitSTOP and GaitFWD and each array has its own set of elements. So far so good then in line 15 you have delcared that the variable Gait1 will be used to reference a 2D array of int, but the assignment part  =GaitFWD does not duplicate the contents of GaitFWD. Instead both Gait1 and GaitFWD refer to the same set of elements.

So in this code you only have two arrays (sets of elements)

1. int  GaitSTOP[][]= {
2.   {O1C, U1C, O2C, U2C, O3C, U3C, O4C, U4C, 200}, 
3.   {O1C, U1C, O2C, U2C, O3C, U3C, O4C, U4C, 200}, 
4.   {O1C, U1C, O2C, U2C, O3C, U3C, O4C, U4C, 200}, 
5.   {O1C, U1C, O2C, U2C, O3C, U3C, O4C, U4C, 200}
6. };  
7. 
   
8. int GaitFWD[][]= {
9.   {O1H, U1C, O2C, U2O, O3C, U3C, O4H, U4O, 200}, 
10.   {O1H, U1C, O2C, U2C, O3C, U3C, O4H, U4C, 200}, 
11.   {O1C, U1O, O2H+10, U2C, O3H-5, U3O, O4C, U4C, 200}, 
12.   {O1C, U1C, O2H+10, U2C, O3H-5, U3C, O4C, U4C, 200}
13. };
    
14. 
    
15. int Gait1[][]=GaitFWD;

Ah. Thanks a lot. I wsa under the impression that I copy the content fromone  array to another. If it only references the array, the result is logical again.