What is the name of this plant, from Bangladesh?
This plant belong to Malvaceae, and the yellow flowers open towards morning to mid-day.
This plant is most-likely Sida rhombifolia or may be Malvastrum tricuspidatum .
From broad leaves it seems not Sida acuta
Check epicalyx ( made up of bracteoles)... is there is no epicalyx then Sida rhombifolia.
If epicalyx is 3, it is Malvastrum tricuspidatum
look also https://en.wikipedia.org/wiki/Sida_rhombifolia,
https://books.google.co.in/books?id=Roi0lwSXFnUC&amp;lpg=PA258&amp;ots=N7DNvrN4UL&amp;dq=malvastrum%20tricuspidatum%203%20epicalyx&amp;pg=PA258#v=onepage&amp;q=malvastrum%20tricuspidatum%203%20epicalyx&amp;f=false
Epicalyx of Malvastrum tricuspidatum :

C= Corolla (all petals), K= Calyx (all sepals), E= Epicalyx the bracteole

3 bracteoles