MATLAB: sparse matrices in matlab anamoly?

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SUMMARY

The discussion clarifies the difference between the MATLAB functions sparse(rand(4)) and sprand(4). The sprand(4) function generates a sparse matrix with random non-zero entries, while sparse(rand(4)) converts a full matrix generated by rand(4) into a sparse matrix. Since the output of rand(4) contains no zero values, the sparse function does not reduce memory allocation effectively. Understanding the definition and purpose of sparse matrices is crucial for proper usage.

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manjuvenamma
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In MATLAB, Why is sparse(rand(4)) not same as sprand(4)? Is it not supposed to be? What is the reason? Please see the interaction in MATLAB pasted below.

sprand(4)

ans =

(1,1) 0.8147

>> rand(4)

ans =

0.9058 0.0975 0.9649 0.4854
0.1270 0.2785 0.1576 0.8003
0.9134 0.5469 0.9706 0.1419
0.6324 0.9575 0.9572 0.4218

>> sparse(ans)

ans =

(1,1) 0.9058
(2,1) 0.1270
(3,1) 0.9134
(4,1) 0.6324
(1,2) 0.0975
(2,2) 0.2785
(3,2) 0.5469
(4,2) 0.9575
(1,3) 0.9649
(2,3) 0.1576
(3,3) 0.9706
(4,3) 0.9572
(1,4) 0.4854
(2,4) 0.8003
(3,4) 0.1419
(4,4) 0.4218
 
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You haven't understood the meaning of sparse matrices. Sparse matrices store only those values that are NOT zero. Thereby, they decrease memory allocation. Your rand(4) function call didn't return any 0 value, so using sparse function on the answer has no affect.
https://in.mathworks.com/help/matlab/ref/sparse.html
 

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