Strange integral result in Simulink

Hi everyone,

I tried to integrate a signal in the Simulink as follows:

• In the first case:

The ld_d signal is blue which is output from a matlab function block. Clearly, its value are negative during the simulation time. However, the integrated signal is positive. I cannot understand how it could happen.

• In the second cas, I tried to save the ld_d to .mat file then load it again into other simulink file and do the integrating. The integrated result in this implementation is negative which I expected.

Could you please explain why the signal ld1 can be positive in the first case.

The following is the result of the first case.

Thanks in advanced!