# ApplyMatrix - projection matrices

Sarah Harrelson shared this question 2 years ago

Hello -

I have a question about the ApplyMatrix command. When I build a 2x2 projection matrix the ApplyMatrix command appears to fail. What am I doing wrong?

I attached a very simple file to demonstrate the situation I'm struggling with.

Thanks! 1

GG suppose c' is a conic but your matrix has determinant equal to 0. try with no singular matrix 2

Does writing the conic as a parametric curve help to get what you expect, with a transformation with det(Proj)=0 ? 1

or use a polygon for illustrating the transformation 1

Thank you all so much for your suggestions. I had figured the fact that the matrix was singular was the problem. To confirm - applying a singular matrix to a conic or region requires working around the ApplyMatrix command, correct?

Simona your file was very helpful; thank you.

Mathmagic you suggested I use a polygon, but when I similarly attempt to use ApplyMatrix with a projection matrix applied to a polygon I also get an incorrect result. 1

`Mathmagic you suggested I use a polygon, but when I similarly attempt to use ApplyMatrix with a projection matrix applied to a polygon I also get an incorrect result.`

what matrix? what polygon?

if the matrix is singular the polygon is transformed in several segments. 1

Perhaps I misspoke. Here's a sample file. You can see that the projection appears in the algebra screen, but does not show up as a segment in the graphics screen unless I click on it.  1

when you hide the segments then the segments are not visible

move the sliders

Files: foro.ggb