I would suggest to check the matrix dimensions to identify which one is for Height or lambda. You can dirfectly plot the numbers (eg, use 1:N_height and 1:N_lambda) to plot, wherer N_ is the dimension length. Please check the command from matlab as different command may arrange the data differently.
Usually if you save the dataset from Lumerical to .mat then in matlab the read the data as it is. Since this is 3rd party tool it is hard for us to check for it.
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