Code Generation for Sparse Matrices
Sparse matrices provide efficient storage in memory for arrays with many zero elements. Sparse matrices can provide improved performance and reduced memory usage for generated code. Computation time on sparse matrices scales only with the number of operations on nonzero elements.
Functions for creating and manipulating sparse matrices are listed in Sparse Matrices. To check if a
function is supported for code generation, see the function reference page. Code generation
does not support sparse matrix inputs created by using
sparse for all functions.
You can use
coder.typeof to initialize a sparse matrix input to
your function. For sparse matrices, the code generator does not track upper bounds for
variable-size dimensions. All variable-size
dimensions are treated as unbounded.
You cannot define sparse input types programmatically by using
Code Generation Guidelines
Initialize matrices by using sparse constructors to maximize your code efficiency. For
example, to construct a 3-by-3 identity matrix, use
Indexed assignment into sparse matrices incurs an overhead compared to indexed assignment into full matrices. For example:
S = speye(10); S(7,7) = 42;
As in MATLAB®, sparse matrices are stored in compressed sparse column format. When you insert a new nonzero element into a sparse matrix, all subsequent nonzero elements must be shifted downward, column by column. These extra manipulations can slow performance. See Accessing Sparse Matrices.
Code Generation Limitations
To generate code that uses sparse matrices, dynamic memory allocation must be enabled. To store the changing number of nonzero elements, and their values, sparse matrices use variable-size arrays in the generated code. To change dynamic memory allocation settings, see Control Memory Allocation for Variable-Size Arrays. Because sparse matrices use variable-size arrays for dynamic memory allocation, limitations on Variable-Size Data also apply to sparse matrices.
You cannot assign sparse data to data that is not sparse. The generated code uses
distinct data type representations for sparse and full matrices. To convert to and from
sparse data, use the explicit
You cannot define a sparse matrix with competing size specifications. The code
generator fixes the size of the sparse matrix when it produces the corresponding data
type definition in C/C++. As an example, the function
foo causes an
error in code generation:
function y = foo(n) %#codegen if n > 0 y = sparse(3,2); else y = sparse(4,3); end
Logical indexing into sparse matrices is not supported for code generation. For example, this syntax causes an error:
S = magic(3); S(S > 7) = 42;
For sparse matrices, you cannot delete array elements by assigning empty arrays:
S(:,2) = ;