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This is a vector field of dynamical system.
How can this directions be explained?
i seem not to understand this at all.
I am not sure what exactly you mean by "how it can be explained", what you expect as answer and how your question relates to Mathcad.
The only place I've ever used a vector field plot was for magnetic field strength.
Typically, the tail of the vector is at the (x,y) location of the evaluation, the length of the vector is proportional to the magnitude of the quantity, and the arrow is tangent to the direction of the field. (Magnetic field is a vector with components in the x and y directions.)
What your image is a plot of I cannot say, so interpretation is not something I want to attempt. It looks like you have two images--there's a clear edge slightly left of center.
Was this plot created with Mathcad at all? Doesn't seem likely, because a vector field plot in Mathcad only has streight arrows, many of the arrows in your plot are curved.
This - may - be a vector field plot, created from an ideal system model that incorrectly models a real system.
Notice how arrows are pointing in opposite directions from a line at x=-0.7 . As such that line is a source for y>0 and a pit for y<0; another source is at (0,0).
Success!
Luc