Unexpected behavior with From Workspace block in Simulink

The From Workspace block for Simulink is supposed to output data based on the time column in the variable. I have a model at a sample rate 5 times faster than the From Workspace, ie: 0.05 for Data, 0.001 for Model.

When I record the data from the From Workspace block at the Model sample rate of 0.001, I mostly see the data repeated 5 times but sometimes I see it repeated 6 times followed by 4 times for the next. This creates errors in my calculations because the expected data is wrong:

ie, 0 0 0 0 0 1 1 1 1 1 2 2 2 2 2 2 <- extra "2" 3 3 3 3 too little "3" 4 4 4 4 4

Answer 1

[Kaustubha Govind]

(I presume you meant that 0.01 is your model's sample rate, because 0.05 is 50 times 0.001, not 5 times)

This looks like an floating-point/accuracy issue - 0.05*3 is slightly larger than 0.01*15:

>> format hex
>> 0.01*15   

ans =

     3fc3333333333333

>> 0.05*3    

ans =

     3fc3333333333334

Which is why, for the 15th sample, the previous data point (=2) is used.

Perhaps you can adjust the time column of the imported variable so that it is multiples of 0.01 instead of 0.05?

[Thomas Marullo]

Sorry, you are indeed correct. From Workspace block is 0.005000000000000 and model sample rate is 1.000000000000000e-03. I think your recommendation of changing the From Workspace block to be multiples of the model sample rate is a good method.

[Thomas Marullo]

I also tried using 0.04 as my From Workspace timing and 0.01 as my model sample rate and I had the same problems at step 40. I didn't think there would be a problem using this case since,

>> 0.01*40

ans =

     3fd999999999999a

>> 0.04*10

ans =

     3fd999999999999a