Unknown purple flower

i don't know the name of this flower but i like how bright they are. one of my neighbour used to have a lot of them. this plant actually grows quite large.
so they don't have them anymore, but a few months ago a few seeds i brought into my garden, set them below a mango tree, and what do you konw, they are even growing in the shade of the tree.
i guess they don't require much sunlight. i can't plant them on the roof because all my tobs are really small