matlab 画箭头

使用如下命令
ANNOTATION creates an annotation object
ANNOTATION(ANNOTATIONTYPE) creates a default annotation of type
ANNOTATIONTYPE in the current figure. ANNOTATIONTYPE may be one of the
following:
'rectangle'
'ellipse'
'textbox'
'line'
'arrow'
'doublearrow' = two headed arrow
'textarrow' = arrow with text at tail end

ANNOTATION('rectangle',POSITION) creates a rectangle annotation at the
position specified in normalized figure units by the vector POSITION
ANNOTATION('ellipse',POSITION) creates an ellise annotation at the
position specified in normalized figure units by the vector POSITION
ANNOTATION('textbox',POSITION) creates a textbox annotation at the
position specified in normalized figure units by the vector POSITION