times, .*

Element-wise quaternion multiplication

Since R2021a

Syntax

quatC = A.*B

Description

quatC = A.*B returns the element-by-element quaternion multiplication of quaternion arrays.

You can use quaternion multiplication to compose rotation operators:

• To compose a sequence of frame rotations, multiply the quaternions in the same order as the desired sequence of rotations. For example, to apply a p quaternion followed by a q quaternion, multiply in the order pq. The rotation operator becomes $${\left(pq\right)}^{\ast }v\left(pq\right)$$, where v represents the object to rotate in quaternion form. * represents conjugation.

• To compose a sequence of point rotations, multiply the quaternions in the reverse order of the desired sequence of rotations. For example, to apply a p quaternion followed by a q quaternion, multiply in the reverse order, qp. The rotation operator becomes $$\left(qp\right)v{\left(qp\right)}^{\ast }$$.

Examples

Multiply Two Quaternion Vectors

Create two vectors, A and B, and multiply them element by element.

A = quaternion([1:4;5:8]);
B = A;
C = A.*B

C = 2x1 quaternion array
     -28 +   4i +   6j +   8k
    -124 +  60i +  70j +  80k

Multiply Two Quaternion Arrays

Create two 3-by-3 arrays, A and B, and multiply them element by element.

A = reshape(quaternion(randn(9,4)),3,3);
B = reshape(quaternion(randn(9,4)),3,3);
C = A.*B

C = 3x3 quaternion array
     0.60169 +  2.4332i -  2.5844j + 0.51646k    -0.49513 +  1.1722i +  4.4401j -   1.217k      2.3126 + 0.16856i +  1.0474j -  1.0921k
     -4.2329 +  2.4547i +  3.7768j + 0.77484k    -0.65232 - 0.43112i -  1.4645j - 0.90073k     -1.8897 - 0.99593i +  3.8331j + 0.12013k
     -4.4159 +  2.1926i +  1.9037j -  4.0303k     -2.0232 +  0.4205i - 0.17288j +  3.8529k     -2.9137 -  5.5239i -  1.3676j +  3.0654k

Note that quaternion multiplication is not commutative:

isequal(C,B.*A)

ans = logical
   0

Multiply Quaternion Row and Column Vectors

Create a row vector a and a column vector b, then multiply them. The 1-by-3 row vector and 4-by-1 column vector combine to produce a 4-by-3 matrix with all combinations of elements multiplied.

a = [zeros("quaternion"),ones("quaternion"),quaternion(randn(1,4))]

a = 1x3 quaternion array
           0 +       0i +       0j +       0k           1 +       0i +       0j +       0k     0.53767 +  1.8339i -  2.2588j + 0.86217k

b = quaternion(randn(4,4))

b = 4x1 quaternion array
      0.31877 +   3.5784i +   0.7254j -  0.12414k
      -1.3077 +   2.7694i - 0.063055j +   1.4897k
     -0.43359 -   1.3499i +  0.71474j +    1.409k
      0.34262 +   3.0349i -  0.20497j +   1.4172k

a.*b

ans = 4x3 quaternion array
            0 +        0i +        0j +        0k      0.31877 +   3.5784i +   0.7254j -  0.12414k      -4.6454 +   2.1636i +   2.9828j +   9.6214k
            0 +        0i +        0j +        0k      -1.3077 +   2.7694i - 0.063055j +   1.4897k      -7.2087 -   4.2197i +   2.5758j +   5.8136k
            0 +        0i +        0j +        0k     -0.43359 -   1.3499i +  0.71474j +    1.409k       2.6421 -     5.32i -   2.3841j -   1.3547k
            0 +        0i +        0j +        0k      0.34262 +   3.0349i -  0.20497j +   1.4172k      -7.0663 -  0.76439i -  0.86648j +   7.5369k

Input Arguments

A — Input to multiply

quaternion object | array of quaternion objects | real scalar | array of real numbers

Input to multiply, specified as a quaternion object, an array of quaternion objects of any dimensionality, a real scalar, or an array of real numbers of any dimensionality. Numeric values must be of data type single or double.

A and B must have compatible sizes. In the simplest cases, they can be the same size or one can be a scalar. Two inputs have compatible sizes if, for every dimension, the dimension sizes of the inputs are the same or one of them is 1.

B — Input to multiply

quaternion object | array of quaternion objects | real scalar | array of real numbers

Input to multiply, specified as a quaternion object, an array of quaternion objects of any dimensionality, a real scalar, or an array of real numbers of any dimensionality. Numeric values must be of data type single or double.

A and B must have compatible sizes. In the simplest cases, they can be the same size or one can be a scalar. Two inputs have compatible sizes if, for every dimension, the dimension sizes of the inputs are the same or one of them is 1.

Output Arguments

quatC — Quaternion product

quaternion object | array of quaternion objects

Quaternion product, returned as a quaternion object or an array of quaternion objects.

Algorithms

Quaternion Multiplication by a Real Scalar

Given a quaternion,

$$q=a_{\text{q}}+b_{\text{q}}\text{i}+c_{\text{q}}\text{j}+d_{\text{q}}\text{k,}$$

the product of q and a real scalar β is

$$\beta q=\beta a_{\text{q}}+\beta b_{\text{q}}\text{i}+\beta c_{\text{q}}\text{j}+\beta d_{\text{q}}\text{k}$$

Quaternion Multiplication by a Quaternion Scalar

The definition of the basis elements for quaternions,

$${\text{i}}^2={\text{j}}^2={\text{k}}^2=\text{ijk}=-1,$$

can be expanded to populate a table summarizing quaternion basis element multiplication:

	1	i	j	k
1	1	i	j	k
i	i	−1	k	−j
j	j	−k	−1	i
k	k	j	−i	−1

When reading the table, the rows are read first, for example: ij = k and ji = −k.

Given two quaternions, $$q=a_{\text{q}}+b_{\text{q}}\text{i}+c_{\text{q}}\text{j}+d_{\text{q}}\text{k,}$$ and $$p=a_{\text{p}}+b_{\text{p}}\text{i}+c_{\text{p}}\text{j}+d_{\text{p}}\text{k}$$, the multiplication can be expanded as:

$$\begin{array}{l}z=pq=\left(a_{\text{p}}+b_{\text{p}}\text{i}+c_{\text{p}}\text{j}+d_{\text{p}}\text{k}\right)\left(a_{\text{q}}+b_{\text{q}}\text{i}+c_{\text{q}}\text{j}+d_{\text{q}}\text{k}\right)\\ =a_{\text{p}}{a}_{\text{q}}+a_{\text{p}}{b}_{\text{q}}\text{i}+a_{\text{p}}{c}_{\text{q}}\text{j}+a_{\text{p}}{d}_{\text{q}}\text{k}\\ +b_{\text{p}}{a}_{\text{q}}\text{i}+b_{\text{p}}{b}_{\text{q}}{\text{i}}^2+b_{\text{p}}{c}_{\text{q}}\text{ij}+b_{\text{p}}{d}_{\text{q}}\text{ik}\\ +c_{\text{p}}{a}_{\text{q}}\text{j}+c_{\text{p}}{b}_{\text{q}}\text{ji}+c_{\text{p}}{c}_{\text{q}}{\text{j}}^2+c_{\text{p}}{d}_{\text{q}}\text{jk}\\ +d_{\text{p}}{a}_{\text{q}}k+d_{\text{p}}{b}_{\text{q}}\text{ki}+d_{\text{p}}{c}_{\text{q}}\text{kj}+d_{\text{p}}{d}_{\text{q}}{\text{k}}^2\end{array}$$

You can simplify the equation using the quaternion multiplication table.

$$\begin{array}{l}z=pq=a_{\text{p}}{a}_{\text{q}}+a_{\text{p}}{b}_{\text{q}}\text{i}+a_{\text{p}}{c}_{\text{q}}\text{j}+a_{\text{p}}{d}_{\text{q}}\text{k}\\ +b_{\text{p}}{a}_{\text{q}}\text{i}-b_{\text{p}}{b}_{\text{q}}+b_{\text{p}}{c}_{\text{q}}\text{k}-b_{\text{p}}{d}_{\text{q}}\text{j}\\ +c_{\text{p}}{a}_{\text{q}}\text{j}-c_{\text{p}}{b}_{\text{q}}\text{k}-c_{\text{p}}{c}_{\text{q}}+c_{\text{p}}{d}_{\text{q}}\text{i}\\ +d_{\text{p}}{a}_{\text{q}}k+d_{\text{p}}{b}_{\text{q}}\text{j}-d_{\text{p}}{c}_{\text{q}}\text{i}-d_{\text{p}}{d}_{\text{q}}\end{array}$$

References

[1] Kuipers, Jack B. Quaternions and Rotation Sequences: A Primer with Applications to Orbits, Aerospace, and Virtual Reality. Princeton, NJ: Princeton University Press, 2007.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2021a