% partial derivative
>>df=((1.1)^3-(.9)^3)
df =

    0.6020

>>dfx=df/.2
dfx =

    3.0100

>>% Reduce stepsize
>>df=((1.01)^3-(.99)^3)
df =

    0.0600

>>dfx=df/.02
dfx =

    3.0001

>>exit
 29 flops.