Implementation:Google deepmind Mujoco MjModel Header

Knowledge Sources	Google_deepmind_Mujoco
Domains	C API, Physics Simulation, Data Structures, Model Definition
Last Updated	2026-02-15 04:00 GMT

Overview

Primary C header file that defines the MuJoCo model data structure (mjModel), all associated enumeration types, and global simulation constants.

Description

mjmodel.h is the foundational header of the MuJoCo C API, defining global constants (mjPI, mjMAXVAL, mjMINMU, mjMINIMP, mjMAXIMP, mjMAXCONPAIR, mjMAXTREEDEPTH), size parameters for equation data, actuator parameters, solver references and impedance arrays, and the comprehensive set of enumeration types that control simulation behavior. Key enumerations include mjtDisableBit (19 disable flags for constraints, forces, sensors, etc.), mjtEnableBit (override, energy, fwdinv flags), and numerous type enums for joints, geoms, actuators, sensors, and solver configurations. The mjModel struct itself contains all static model data loaded from MJCF/URDF files.

Usage

This header is included by virtually all MuJoCo C/C++ code and is the primary interface for accessing the model structure. It is also the basis for Python bindings and MJX type definitions that mirror these structures in JAX/Warp.

Code Reference

Source Location

Repository: Google_deepmind_Mujoco
File: include/mujoco/mjmodel.h
Lines: 1-1309

Key Functions

// Global constants
#define mjPI            3.14159265358979323846
#define mjMAXVAL        1E+10     // maximum value in qpos, qvel, qacc
#define mjMINMU         1E-5      // minimum friction coefficient
#define mjMAXCONPAIR    50        // maximum contacts per geom pair
#define mjMAXTREEDEPTH  50        // maximum BVH depth

// Size constants
#define mjNEQDATA       11        // number of eq_data fields
#define mjNDYN          10        // number of actuator dynamics parameters
#define mjNGAIN         10        // number of actuator gain parameters
#define mjNBIAS         10        // number of actuator bias parameters
#define mjNSOLVER       200       // size of one mjData.solver array

// Key enumerations
typedef enum mjtDisableBit_ { ... } mjtDisableBit;   // 19 disable flags
typedef enum mjtEnableBit_ { ... } mjtEnableBit;     // enable optional features

Import

#include <mujoco/mjmodel.h>

I/O Contract

Inputs

Name	Type	Required	Description
(header definitions)	N/A	N/A	No runtime inputs; provides type definitions, constants, and struct declarations

Outputs

Name	Type	Description
mjModel	struct	Complete static model structure containing all physics parameters, kinematic tree, geom definitions, actuators, sensors, and solver settings
mjtDisableBit	enum	Bitflags to selectively disable simulation features (constraints, forces, sensors, etc.)
mjtEnableBit	enum	Bitflags to enable optional features (energy computation, forward-inverse, etc.)
Global constants	#define	Simulation limits and numerical constants

Related Pages

Google_deepmind_Mujoco_MjTnum_Header - Numeric type definitions (mjtNum) included by this header
Google_deepmind_Mujoco_MjSpec_Header - Spec header that includes mjmodel.h for model specification types
Google_deepmind_Mujoco_API_References_Header - Auto-generated API reference enumerations
Google_deepmind_Mujoco_MJX_Warp_Types - MJX Python types that mirror these C structures

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