This example shows how to compute the signed square root of a negative-valued input signal.

ans = 

  Simulink.SimulationOutput:
                   tout: [51x1 double] 

     SimulationMetadata: [1x1 Simulink.SimulationMetadata] 
           ErrorMessage: [0x0 char] 

When the block input is negative and you set the Function to signedSqrt, the Sqrt block output is the same for any setting of the Output signal type parameter. By setting the Format of the first Display block to decimal (Stored Integer), you can see the value of the imaginary part for the complex output.