1.3. Data Types

SUNDIALS defines several data types in the header file sundials_types.h. These types are used in the SUNDIALS API and internally in SUNDIALS. It is not necessary to use these types in your application, but the type must be compatible with the SUNDIALS types in the API when calling SUNDIALS functions. The types that are defined are:

  • sunrealtype – the floating-point type used by the SUNDIALS packages

  • sunindextype – the integer type used for vector and matrix indices

  • sunbooleantype – the type used for logic operations within SUNDIALS

  • SUNOutputFormat – an enumerated type for SUNDIALS output formats

  • SUNComm – a simple typedef to an int when SUNDIALS is built without MPI, or a MPI_Comm when built with MPI.

1.3.1. Floating point types

type sunrealtype

The type sunrealtype can be float, double, or long double, with the default being double. The user can change the precision of the arithmetic used in the SUNDIALS solvers at the configuration stage (see SUNDIALS_PRECISION).

Additionally, based on the current precision, sundials_types.h defines SUN_BIG_REAL to be the largest value representable as a sunrealtype, SUN_SMALL_REAL to be the smallest value representable as a sunrealtype, and SUN_UNIT_ROUNDOFF to be the difference between \(1.0\) and the minimum sunrealtype greater than \(1.0\).

Within SUNDIALS, real constants are set by way of a macro called SUN_RCONST. It is this macro that needs the ability to branch on the definition of sunrealtype. In ANSI C, a floating-point constant with no suffix is stored as a double. Placing the suffix “F” at the end of a floating point constant makes it a float, whereas using the suffix “L” makes it a long double. For example,

#define A 1.0
#define B 1.0F
#define C 1.0L

defines A to be a double constant equal to \(1.0\), B to be a float constant equal to \(1.0\), and C to be a long double constant equal to \(1.0\). The macro call SUN_RCONST(1.0) automatically expands to 1.0 if sunrealtype is double, to 1.0F if sunrealtype is float, or to 1.0L if sunrealtype is long double. SUNDIALS uses the SUN_RCONST macro internally to declare all of its floating-point constants.

Additionally, SUNDIALS defines several macros for common mathematical functions e.g., fabs, sqrt, exp, etc. in sundials_math.h. The macros are prefixed with SUNR and expand to the appropriate C function based on the sunrealtype. For example, the macro SUNRabs expands to the C function fabs when sunrealtype is double, fabsf when sunrealtype is float, and fabsl when sunrealtype is long double.

A user program which uses the type sunrealtype, the SUN_RCONST macro, and the SUNR mathematical function macros is precision-independent except for any calls to precision-specific library functions. Our example programs use sunrealtype, SUN_RCONST, and the SUNR macros. Users can, however, use the type double, float, or long double in their code (assuming that this usage is consistent with the typedef for sunrealtype) and call the appropriate math library functions directly. Thus, a previously existing piece of C or C++ code can use SUNDIALS without modifying the code to use sunrealtype, SUN_RCONST, or the SUNR macros so long as the SUNDIALS libraries are built to use the corresponding precision (see §1.2.2).

1.3.2. Integer types used for indexing

type sunindextype

The type sunindextype is used for indexing array entries in SUNDIALS modules as well as for storing the total problem size (e.g., vector lengths and matrix sizes). During configuration sunindextype may be selected to be either a 32- or 64-bit signed integer with the default being 64-bit (see SUNDIALS_INDEX_SIZE).

When using a 32-bit integer the total problem size is limited to \(2^{31}-1\) and with 64-bit integers the limit is \(2^{63}-1\). For users with problem sizes that exceed the 64-bit limit an advanced configuration option is available to specify the type used for sunindextype (see SUNDIALS_INDEX_TYPE).

A user program which uses sunindextype to handle indices will work with both index storage types except for any calls to index storage-specific external libraries. Our C and C++ example programs use sunindextype. Users can, however, use any compatible type (e.g., int, long int, int32_t, int64_t, or long long int) in their code, assuming that this usage is consistent with the typedef for sunindextype on their architecture. Thus, a previously existing piece of C or C++ code can use SUNDIALS without modifying the code to use sunindextype, so long as the SUNDIALS libraries use the appropriate index storage type (for details see §1.2.2).

1.3.3. Boolean type

type sunbooleantype

As ANSI C89 (ISO C90) does not have a built-in boolean data type, SUNDIALS defines the type sunbooleantype as an int.

The advantage of using the name sunbooleantype (instead of int) is an increase in code readability. It also allows the programmer to make a distinction between int and boolean data. Variables of type sunbooleantype are intended to have only the two values: SUNFALSE or SUNTRUE.


False (0)


True (1)

1.3.4. Output formatting type

enum SUNOutputFormat

The enumerated type SUNOutputFormat defines the enumeration constants for SUNDIALS output formats


The output will be a table of values


The output will be a comma-separated list of key and value pairs e.g., key1,value1,key2,value2,...


The file scripts/sundials_csv.py provides python utility functions to read and output the data from a SUNDIALS CSV output file using the key and value pair format.

1.3.5. MPI types

type SUNComm

A simple typedef to an int when SUNDIALS is built without MPI, or a MPI_Comm when built with MPI. This type exists solely to ensure SUNDIALS can support MPI and non-MPI builds.


A macro defined as 0 when SUNDIALS is built without MPI, or as MPI_COMM_NULL when built with MPI.