For translations, scales, and shears, the subscripts of matrix elements indicate the axis affected by values at that location. The identity matrix transforms any point to itself. This has the effect of applying aTransform 's matrix after the receiver's matrix. Invoking this method defines a new user coordinate system whose coordinates are mapped into the former coordinate system according to the receiver's transformation matrix. To undo the concatenation, you must invert the receiver's matrix and invoke this method again.
Inverse matrices are useful for undoing the effects of a matrix.
You can also use them in conjunction with the concat method to remove the effects of concatenating the matrix to the current transformation matrix of the current graphic context. Multiplies aTransform and the receiver's matrix, and replaces the receiver's matrix with the result. This has the effect of applying aTransform before the receiver's transform. Any previous transformations associated with the matrix are lost and replaced by the rotation. After invoking this method, applying the receiver's matrix will turn the axes counterclockwise about the current origin by angle degrees.