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The CSR format stores a sparse {{math|''m'' × ''n''}} matrix {{math|'''M'''}} in row form using three (one-dimensional) arrays {{math|(V, COL_INDEX, ROW_INDEX)}}. Let {{math|NNZ}} denote the number of nonzero entries in {{math|'''M'''}}. (Note that [[Zero-based numbering|zero-based indices]] shall be used here.)
* The arrays {{math|V}} and {{math|COL_INDEX}} are of length {{math|NNZ}}, and contain the non-zero values and the column indices of those values respectively
* {{math|COL_INDEX}} contains the column in which the corresponding entry {{math|V}} is located.
* The array {{math|ROW_INDEX}} is of length {{math|''m'' + ''1''}} and encodes the index in {{math|V}} and {{math|COL_INDEX}} where the given row starts. This is equivalent to {{math|ROW_INDEX[j]}} encoding the total number of nonzeros above row {{math|j}}. The last element is {{math|NNZ}} , i.e., the fictitious index in {{Math|V}} immediately after the last valid index {{math|NNZ - 1}}. <ref>{{cite book |last1=Saad |first1=Yousef |title=Iterative methods for sparse linear systems |date=2003 |publisher=SIAM}}</ref>
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