Fix description of arguments of csr_to_dense_matrix

Author: mcol

src/functions-reference/sparse_matrix_operations.Rmd

@@ -94,9 +94,11 @@ a single function.
 `matrix` **`csr_to_dense_matrix`**`(int m, int n, vector w, int[] v, int[] u)`<br>\newline
 Return dense $\text{m} \times \text{n}$ matrix with non-zero matrix
 entries w, column indices v, and row starting indices u; the vector w
-and arrays v and u must all be the same size, and the arrays v and u
-must have index values bounded by m and n. see section [compressed row storage](#CSR) for
-more details.
+and array v must be the same size (corresponding to the total number of
+nonzero entries in the matrix), array v must have index values bounded
+by m, array u must have length equal to m + 1 and contain index values
+bounded by n (except for the last entry, which should be equal to one plus
+the length of w). See section [compressed row storage](#CSR) for more details.
 
 ## Sparse Matrix Arithmetic
 
@@ -116,4 +118,3 @@ rather than $A$ as a sparse matrix.
 Multiply the $\text{m} \times \text{n}$ matrix represented by values
 w, column indices v, and row start indices u by the vector b; see
 [compressed row storage](#CSR).
-