why current is different at the same voltage?

[lida]

Dear all:
       Now I am facing a new problem like this, I hope you can give some help:
       When I calculated the I-V character of Au-Si two probe system in many different voltages, I set the voltages using the following fomat:
       for voltage in numpy.linspace(0.0,2.0,10)*Volt
       And then, I got the currents at every voltage points.
       However, if I set the voltages separately, that is I calculated one current in relevant voltage a time, I got another current value, this current is much smaller than the previous one at the same voltage. For example, at the given voltage of 1.8V, calculated in [for voltage in numpy.linspace(0.0,2.0,10)*Volt], the current is about 120000nA, calculated with only one point voltage at one time, the currrent is about 25000nA, the latter one is much smaller. Why do this happen? This puzzle me a lot.
      Additional, did the direct of applied voltage in electrode have some effect on current magnitude, or it just affect the current direct?
     Thank you for your reply.
     Sincerely, lida.

[anyuezhiji]

 It'seems that just [for voltage in numpy.linspace(0.0,2.0,11)*Volt] contains 1.8 v .

[Anders Blom]

That would be one explanation, indeed. Another might be that you apply the voltage the opposite way when you do it manually, or something else. It's very difficult to tell without more precise details, how the scripts were set up, etc.