You cannot have two different data types in one cell. I can see you're attempting to convert a number (I presume of type double) to a string, add some text and then want the overall string to be presented in a single cell in the table. I suggest trying num2str():
ipat = ['The Indicated Power at ', num2str(app.IPat), ' kW'];
I have no idea what app.T is, so I cannot advise on what app.UITable.Data = [app.T ; ipat] will acheive. Though if you only want the phrase (for example) "The Indicated Power at 100 kW" to be shown, then try:
app.UITable.Data = ipat;
