1Applying Matlab 21/30/20082Opening Discussion■What did we talk about last class?■Do you have any questions about the reading?■Using end for indexing.3Control Flow Constructs■Last time we looked at the for loop. We also have the following:While loopIf statements – includes if, else, end, and elseif.Switch-case – allows cases with multiple expressions and otherwise clause.Try-catch blocks for error handling. Variable lasterr gives information about the last error.■In general you can get away with only using loops and the if conditional. Switch is occasionally helpful and the try-catch is nice in situations where something might go wrong.4Examples of Control Flow■Write a few lines of code that will do Serpinski's triangle and put each new point in a single Nx2 array. Put 5000 points into it.■You can plot that array with the following:plot(data(:,1),data(:,2),'.')Now write a loop that will do a Mandelbrot check for a single point. Have it loop until zn has a magnitude greater than 2 or you get through 100 iterations.5Functions■Matlab functions are a bit different from what you are used to in other languages. They can take a variable number of arguments and return a variable number of arguments.■To return a value, we set a variable with the name specified on the first line of the function to the value we want to return. That is what will be returned when the function terminates.■You can also have local functions or nested functions. When either of these is used the main function must be terminated with end.■Function handles are also discussed in the book and they are worth noting.6Writing a Function■We have our Matlab code to do the iteration for a single pixel of the mandelbrot set. Now make an m-file and put that code into the m-file as a function that takes a point and returns how many iterations it went.■Let's try to write code that will plot up a full Mandelbrot set for us.7Multidimensional Arrays■Arrays in Matlab can have more than 2 dimensions to them.■We aren't going to deal with these much in this course and your book doesn't really deal with them outside of this one chapter either.8Numeric Data Types■By default, everything in Matlab is a double. However, you can force things to be other types.■Integer types can be signed or unsigned with 8, 16, 32, or 64 bits. When you construct an array with one of the construction methods, you can pass in a string giving the integer type. The class function lets you see the type of something that you have.■You can also do a casting like operation to make something a particular type.■If you want, there are also single precision floating point numbers.9Cell Arrays■You make these with {} or the cell function. They don't have to be rectangular and they can hold any data. Each cell can hold a different type of data.■We can index into cell arrays with {} as well. If you index a cell array with () you get a cell containing data. If you use {} you get the data that was in the cell.■Multiple elements can't normally be pulled out with content addressing unless you put them into multiple variables with a comma separated list.■Anything that produces multiple cells will be turned into a comma separated list. This can be difficult to get your brain around.10Structures■You can use the dot notation to put fields into a variable to make a structure. Unlike normal imperative languages, the format of the structure isn't predefined.■Matlab deals with arrays of structures just like numeric arrays.■The struct function can build arrays of structures from existing cell arrays.■You can pull out all the values of certain field with 'dynamic addressing'.11Strings■Like most other languages, Matlab does give you the ability to use strings, though that isn't a real strength.■A Matlab string is simply a row array of characters.■A downside of this is that an array with multiple strings must have all the strings be the same length. The char function can help with that.■You can also convert from numbers to strings and back with str2num and num2str.■Matlab also has fprintf and sprintf functions that work much like the C functions.■Similarly, sscanf will pull numbers out of strings.■eval and evalc let you process a string like it were a Matlab function.12Closing Remarks■Remember to submit assignment #2
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