Implement a matvec method for the DEN matrix class

[KyleVaughn]

Description:

The purpose of this issue is to implement a matvec method for the DEN matrix class. This method, is responsible for carrying out the matrix vector multiplication for the a 2-dimensional array stored in as a dense matrix where each element is populated with either non-zero values or with zero values. The function interface is virtual fp_type matvec(fp_type vecin)

After input, we process matrix vector multiplication as follows where the statement below is placed in a nested for loop that iterates for all elements in a[i][j]: b[i]=a[i][j]*x[j]

Tasks:

• Create a function that takes in the parameters sent during function call. These inputs are our 2-dimensional array A, vector B and the number of rows and columns. The inputs would be passed as pointers and hence do not necessitate the need for being returned at the end of this method.
• Checks that all the input parameters have been appropriately passed. If not, pass an error. An example of an incorrect input is having negative numbers for the size of the matrix.
• Perform matrix vector multiplication. This would be done in a try and catch block and throw any errors encountered during matrix vector multiplication. Examples of errors that would be caught in this block are mismatch between matrix and vector size or errors due to insufficient memory allocation.

Definition of done:

Provided function is capable of performing matrix vector multiplication as required with the parameters that have been sent during the function call period.

[KyleVaughn]

Review by @preetb1199

Overall the description and definition looks details and precise. One important factor to considered that is missed is that there should be a check for the size of vector and the matrix because it is necessary the the number of elements in vector should be equal to the number of columns in the matrix for the correct matvec implementation.

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[Lazy-Beee]

I would suggest using the function interface virtual fp_type* matvec(fp_type* vecin) and I'll add this to the SparseMatrix class.

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Edit: change the api to avoid memory leak void matvec(fp_type* vecin, fp_type* vecout)