Implementation:Google deepmind Mujoco Engine Util Misc

Knowledge Sources	Google_deepmind_Mujoco
Domains	Physics Simulation, Utility Functions
Last Updated	2026-02-15 04:00 GMT

Overview

Implements miscellaneous utility functions for the MuJoCo engine, including tendon wrapping, muscle dynamics, contact force encoding, history buffers, type conversion, and general-purpose numerical helpers.

Description

This large utility file contains a diverse collection of functions used across the MuJoCo engine. Key subsystems include tendon wrapping around spheres and cylinders with 2D circle/line intersection calculations, muscle gain/bias/dynamics computations, contact force pyramid encoding and decoding, history buffer management for time-series interpolation, and type conversion between mjtNum, float, and double. It also provides general-purpose functions such as min/max/clip/sign, sorting, random number generation, gather/scatter operations, Base64 encoding/decoding, and formatted matrix printing.

Usage

These utility functions are called throughout the engine for tendon path computation, actuator force generation, contact processing, data type conversions, and various numerical helper operations.

Code Reference

Source Location

Repository: Google_deepmind_Mujoco
File: src/engine/engine_util_misc.c
Lines: 1-1900

Key Functions

// Tendon wrapping
mjtNum mju_wrap(mjtNum wpnt[6], const mjtNum x0[3], const mjtNum x1[3],
                const mjtNum xpos[3], const mjtNum xmat[9],
                mjtNum radius, int type, const mjtNum side[3]);

// Muscle dynamics
mjtNum mju_muscleGain(mjtNum len, mjtNum vel, const mjtNum lengthrange[2],
                      mjtNum acc0, const mjtNum prm[9]);
mjtNum mju_muscleBias(mjtNum len, const mjtNum lengthrange[2],
                      mjtNum acc0, const mjtNum prm[9]);
mjtNum mju_muscleDynamics(mjtNum ctrl, mjtNum act, const mjtNum prm[3]);

// Contact force encoding
void mju_encodePyramid(mjtNum* pyramid, const mjtNum* force,
                       const mjtNum* mu, int dim);
void mju_decodePyramid(mjtNum* force, const mjtNum* pyramid,
                       const mjtNum* mu, int dim);

// History buffers
void mju_historyInit(mjtNum* buf, int n, int dim,
                     const mjtNum* times, const mjtNum* values, mjtNum user);
mjtNum* mju_historyInsert(mjtNum* buf, int n, int dim, mjtNum t);

// Miscellaneous
mjtNum mju_min(mjtNum a, mjtNum b);
mjtNum mju_max(mjtNum a, mjtNum b);
mjtNum mju_clip(mjtNum x, mjtNum min, mjtNum max);
const char* mju_type2Str(int type);
int mju_str2Type(const char* str);

Import

#include "engine/engine_util_misc.h"

I/O Contract

Inputs

Name	Type	Required	Description
x0, x1, xpos	mjtNum[3]	Yes	3D positions for wrapping endpoints and obstacle center
radius	mjtNum	Yes	Radius for wrapping sphere or cylinder
len, vel	mjtNum	Yes	Muscle length and velocity for dynamics
prm	mjtNum*	Yes	Parameter arrays for muscle or spring-damper models
type	int	Yes	Object type identifier (mjtObj enum value)

Outputs

Name	Type	Description
wpnt	mjtNum[6]	Computed wrapping points (pair of 3D points)
return value	mjtNum	Computed wrapping length, muscle force, or utility result
pyramid, force	mjtNum*	Encoded/decoded contact force representation

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