Change column in matrix

Hello,

I got matrix 3x3

Code:

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double matrix[3][3]={{0}, {0}, {0}};
double vector[3]={7,7,7};

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how to put the vector on the first column of my matrix?
do I understand correctly that matrix[0] is an adress to the first column?
i would like to change the adress of first column to the adress of the vector.

Quote:

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Originally Posted by plasticstone

Hello,

I got matrix 3x3

Code:

---

double matrix[3][3]={{0}, {0}, {0}};
double vector[3]={7,7,7};

---

how to put the vector on the first column of my matrix?

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Use a for loop and assign every element of vector to the corresponding elements of matrix:

Code:

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matrix[0][i] = vector[i];

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Quote:

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do I understand correctly that matrix[0] is an adress to the first column?

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Yes, that's correct, but arrays are not modifiable values. matrix[0] is an array of 3 doubles (remember, it's a 2-d array). Thus you can't change where matrix[0] points.

Quote:

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i would like to change the adress of first column to the adress of the vector.

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Like I said, you can't change the address of the first column. You would need a 1-d array of pointers (double *matrix[3]; ) to do that, but it's not a very good approach. It will become very difficult to keep track of what's in matrix.

Quote:

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Originally Posted by plasticstone

Hello,
how to put the vector on the first column of my matrix?

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It depends on how do you interpret rows and columns but:

Code:

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int i;

for (i = 0; i < 3; i++){
    matrix[i][0] = vector[i];
}

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Quote:

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Originally Posted by plasticstone

do I understand correctly that matrix[0] is an adress to the first column?

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Again, "It depends on how do you interpret rows and columns", but since C is row-major, no matrix[0] is the address of the first row.

Quote:

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Originally Posted by plasticstone

i would like to change the adress of first column to the adress of the vector.

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You can't do that, not in this way. Using an array of pointers is a workaround, but not a pretty one.