[Ipe-discuss] Ellipse: transformation matrix must be transposed?

[Pennings, Gijs]

I'm using IPE to draw ellipses, but I don't fully understand the path representation.

Consider the ellipse described by x^2/4 + y^2/36 = 1, and rotate it counterclockwise by pi/6. Then, we compute the transformation matrix by multiplying the rotation matrix with the scale matrix (the operations are applied right to left). I find A = ((1.732, -3), (1, 5.196)). This seems correct; see the attached screenshot.

However, to get the desired result in IPE, it seems that this matrix must be transposed (i.e., specified as the path "1.732 1 -3 5.196 0 0 e"). Otherwise, the ellipse isn't rotated (since rotation would be applied first, which has no effect on a unit circle?).
Is this observation correct and is it intended behavior? I couldn't find it in the manual: https://otfried.github.io/ipe/90_file_format.html?highlight=ellipse#path-construction-operators.

Thanks,
Gijs
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