From what you are describing as requirements, you are correct that you need to use the 'Lookup Table Dynamic' block. You are also correct that the requirements of this block specify that the xdat input vector must be strictly monotonically increasing. This constraint arises from the fact that the lookup table models a proper function. If you have a non-unique lookup for the same x-value, then a lookup table cannot uniquely determine the output value.
My recommendation is that you sort your x table data and then correspondingly use the sorted indices to sort your y table data. With your vectors monotonically sorted, you can directly use the 'Lookup Table Dynamic' block. The Sort and Permute Matrix Simulink blocks seem to be the most straightforward method of implementing my suggestion. Note: the Permute Matrix block is part of the DSP System Toolbox.
To help you get started, here is a simple Simulink model that would allow you to use the Dynamic Lookup block:
Hope this helps!
