Package jsim.core

Class Mat3

java.lang.Object
jsim.core.Mat3
public final class Mat3 extends Object
Internal row-major 3x3 matrix math for deterministic physics.

Index layout: [0 1 2 / 3 4 5 / 6 7 8] where row r, col c = index r*3+c.

  • Method Summary

    Modifier and Type
    Method
    Description
    static double[]
    diagonal(double a, double b, double c)
    Returns a diagonal 3x3 matrix with the given diagonal elements.
    static double[]
    fromQuaternion(double qw, double qx, double qy, double qz)
    Build rotation matrix from unit quaternion (w, x, y, z).
    static double[]
    identity()
    Returns the 3x3 identity matrix as a 9-element row-major array.
    static double[]
    invert(double[] m)
    Invert a 3x3 matrix using Cramer's rule.
    static double[]
    mul(double[] a, double[] b)
    Multiply two 3x3 row-major matrices (a * b).
    static double[]
    mulVec(double[] m, double[] v)
    Multiply a 3x3 matrix by a 3-vector (m * v).
    static double[]
    rotateInertia(double[] R, double d0, double d1, double d2)
    Compute R * diag(d0,d1,d2) * R^T efficiently.
    static double[]
    transpose(double[] m)
    Transpose of a 3x3 row-major matrix.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Method Details

    • identity

      public static double[] identity()
      Returns the 3x3 identity matrix as a 9-element row-major array.
      Returns:
      identity matrix

    • diagonal

      public static double[] diagonal(double a, double b, double c)
      Returns a diagonal 3x3 matrix with the given diagonal elements.
      Parameters:
      a - first diagonal element
      b - second diagonal element
      c - third diagonal element
      Returns:
      9-element row-major diagonal matrix

    • fromQuaternion

      public static double[] fromQuaternion(double qw, double qx, double qy, double qz)
      Build rotation matrix from unit quaternion (w, x, y, z).
      Parameters:
      qw - quaternion W component
      qx - quaternion X component
      qy - quaternion Y component
      qz - quaternion Z component
      Returns:
      3x3 row-major rotation matrix as a 9-element array

    • mulVec

      public static double[] mulVec(double[] m, double[] v)
      Multiply a 3x3 matrix by a 3-vector (m * v).
      Parameters:
      m - 3x3 row-major matrix (9 elements)
      v - input vector (3 elements)
      Returns:
      result vector (3 elements)

    • mul

      public static double[] mul(double[] a, double[] b)
      Multiply two 3x3 row-major matrices (a * b).
      Parameters:
      a - left matrix (9 elements)
      b - right matrix (9 elements)
      Returns:
      product matrix (9 elements)

    • transpose

      public static double[] transpose(double[] m)
      Transpose of a 3x3 row-major matrix.
      Parameters:
      m - input matrix (9 elements)
      Returns:
      transposed matrix (9 elements)

    • rotateInertia

      public static double[] rotateInertia(double[] R, double d0, double d1, double d2)
      Compute R * diag(d0,d1,d2) * R^T efficiently. Used to transform body-frame diagonal inertia to world frame.
      Parameters:
      R - rotation matrix (9 elements, row-major)
      d0 - first diagonal element
      d1 - second diagonal element
      d2 - third diagonal element
      Returns:
      3x3 result matrix (9 elements)

    • invert

      public static double[] invert(double[] m)
      Invert a 3x3 matrix using Cramer's rule. Returns the identity matrix if the input is singular.
      Parameters:
      m - input matrix (9 elements, row-major)
      Returns:
      inverted matrix (9 elements)