Finding MATLAB Errors

An important lesson you can learn about using MATLAB is how to find errors. One common error message from MATLAB is  

This means that q is either an undefined function or an undefined variable. If q is a function or m-file, then MATLAB cannot find it. Check the working directory or use set path and make sure that the path is set to the folder where you stored the m-file and that you have added that path to the list. Do not forget to save your pathlist so that it is there the next time you use MATLAB. If q is a variable, it has not been set or was not transferred correctly. 

One source of confusion is when you think you have defined a variable, but have not really. Use disp(x) to see the current value of x in the command workspace. If the variable is supposed to be in an m-file, run the m-file with a command added to display the variable, and that will give you the value of x in the m-file workspace. That should give you a hint about possible sources of the error. The most common cause of this mistake (and one that is hard to find unless you check the code systematically) is forgetting to pass a parameter to the m-file using either global or as a parameter. The reason it is hard to find these mistakes is that in your mind you have set the value of the parameter in the program somewhere but failed to transfer it to the appropriate m-file. 

This message means that a matrix like was called with either i or j too big (i.e., 

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When you use MATLAB, your results will only be as good as the programs you write. Thus, it is important to understand the stracture of workspaces and m-files, as well as how to display intermediate results, transfer parameters from one m-file to another, and debug your code. Most of the problems encountered by beginning users involve errors in these areas, and only careful checking will help you find them. 

With a trial -error search of K and a eith MATLAB, ire find a possible set of K and a as follcwsx... 

You will find that you will seldom get your scripts to run correctly the first time. However, you should not panic, as this is also the case for experienced programmers. You will need to learn to identify and correct the errors, known in computer jargon as bugs. Before we move to the types of errors involved in MATLAB scripting and programming, let us introduce the concept of representing number, in particular for non-integer numbers. 

Use Excel with a starting point (1,0) to find values of ti and T2 that minimize the sum of squares of the errors. Compare your answer with that obtained using MATLAB. 

First, Equation 11.55 was solved in order to find the hydrocracking kinetic model parameters a, Oq, a, 8, and Then, by using these values. Equation 11.71 was resolved and the parameters p, and were found. All routines were written in MATLAB software. The criterion of minimization of the sum of square errors (SSE) obtained from the difference of calculated and experimental points was employed to determine all model parameters. More details of numerical solution of Equation 11.55 can be found elsewhere (Elizalde and Ancheyta, 2011). 

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