scipy.optimize.least_squares for more than one dimension?

[Martin Schöön]

Yesterday I wanted to move from optimize.leastsq to 
least_squares. I have data depending on four variables
and want to fit a function in four variables to this
data. This works with leastsq but not with least_squares.

Am I trying to do something least_squares is not capable
of?

Disclaimer: I was burning midnight oil...

TIA

/Martin