Matrices

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GeoGebra supports real matrices, which are represented as a list of lists that contain the rows of the matrix.

Example: In GeoGebra, {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}} represents the 3x3 matrix \mathrm{\mathsf{ \begin{pmatrix}1&2&3\\ 4&5&6\\ 7&8&9 \end{pmatrix} }}


To display a matrix using LaTeX formatting in the Menu view graphics.svg Graphics View, use the FormulaText command or drag and drop the matrix definition from Algebra View to Graphics View.

Example: In the Input Bar type FormulaText[{{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}] to display the matrix using LaTeX formatting.


Accessing Elements of Matrices

To access particular elements of a matrix you can use the Element Command or the simplified syntax shown in the example below:

Example: Let matrix={{1, 2}, {3, 4}}, then:
  • matrix(1, 1) returns the first element in the first line: 1
  • matrix(2, 2), matrix(-1,2), matrix(2,-1) and matrix(-1,-1) all return the second element of the second line: 4.
  • In general, matrix(i, j) , where i and j are integers, returns the element of the matrix that occupies the i-th row and the j-th column.


Matrix Operations

Matrix operations are operations with lists, so the following syntaxes produce the described results.

Note: Some syntaxes can represent operations which are not defined in the same way in the matrices set.

Addition and subtraction

  • Matrix1 + Matrix2: adds the corresponding elements of two compatible matrices.
  • Matrix1 – Matrix2: subtracts the corresponding elements of two compatible matrices.

Multiplication and division

  • Matrix * Number: multiplies each element of Matrix by the given Number.
  • Matrix1 * Matrix2: uses matrix multiplication to calculate the resulting matrix.
Note: The rows of the first and columns of the second matrix need to have the same number of elements.
Example: {{1, 2}, {3, 4}, {5, 6}} * {{1, 2, 3}, {4, 5, 6}} yields the matrix {{9, 12, 15}, {19, 26, 33}, {29, 40, 51}}.
  • 2x2 Matrix * Point (or Vector): multiplies the Matrix by the given Point / Vector and yields a point.
Example: {{1, 2}, {3, 4}} * (3, 4) yields the point A = (11, 25).
  • 3x3 Matrix * Point (or Vector): multiplies the Matrix by the given Point / Vector and yields a point.
Example: {{1, 2, 3}, {4, 5, 6}, {0, 0, 1}} * (1, 2) gives you the point A = (8, 20).
Note: This is a special case for affine transformations where homogeneous coordinates are used: (x, y, 1) for a point and (x, y, 0) for a vector. This example is therefore equivalent to: {{1, 2, 3}, {4, 5, 6}, {0, 0, 1}} * {1, 2, 1}.
  • Matrix1 / Matrix2: Divides each element of Matrix1 by the corresponding element in Matrix2.
Note: However, GeoGebra supports the syntax Matrix1 * Matrix2 ^(-1) .

Other operations

The section Matrix Commands contains the list of all available commands related to matrices, such as:

  • Determinant[Matrix]: calculates the determinant for the given matrix.
  • Invert[Matrix]: inverts the given matrix
  • Transpose[Matrix]: transposes the given matrix
  • ApplyMatrix[Matrix,Object]: apply affine transform given by matrix on object.
  • ReducedRowEchelonForm[Matrix]: converts the matrix to a reduced row-echelon form


Comments

Note: See the official forum for a more detailed discussion about the multiplication of matrices.
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