Download MATLAB Compiler User`s Guide

Type Imputation
Type Imputation
The MATLAB interpreter views all variables in M-files as a single object type
— the MATLAB array. All MATLAB variables, including scalars, vectors,
matrices, strings, cell arrays, and structures are stored as MATLAB arrays.
The mxArray declaration corresponds to the internal data structure that
MATLAB uses to represent arrays. The MATLAB array is the C language
definition of a MATLAB variable.
To generate efficient C code from an M-file, the MATLAB Compiler analyzes
how the variables in the M-files are assigned values and how these values are
used. The goal of this analysis is to determine which variables can be
downsized to a smaller data type (a C int or a C double). This analysis process
is called type imputation; the MATLAB Compiler imputes a data type for a
variable. For example, if the MATLAB Compiler sees
[m,n] = size(a);
then the MATLAB Compiler probably imputes the C int type for variables m
and n because in MATLAB the result of this operation always yields integer
scalars.
In some cases, the MATLAB Compiler has to read several lines of code in order
to impute properly. For example, if the MATLAB Compiler sees
[m,n] = size(a);
m = m + .25;
then the MATLAB Compiler imputes the C double data type for variable m.
Note: Specifying assertions and pragmas, as described later in this chapter,
can greatly assist the type imputation process.
Type Imputation Across M-Files
If an M-file calls another M-file function, the MATLAB Compiler reads the
entire contents of the called M-file function as part of the type imputation
4-3