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The notation used to represent the structure in MatLab is struct which can be a single field, no field, or multiple fields. Each field has different data types and a single field must have the same kind of data. Otherwise it behaves like a cell array (although the syntax for using it is completely different). A structure in MatLab is a data type that is used to group the related data types using the data containers known as fields. Those names are then converted to a numerical index behind-the-scenes. MATLAB can't use the optimized libraries and processor instructions.Ī structure is a special type of cell array where the index along one dimension uses names instead of numbers. Because of this, they can "hold" any value, but they lose the speed advantage. These could be individual values or other arrays (including other cell arrays). This is why growing an array is slow in MATLAB, MATLAB has to create an entire new block of memory and copy all the values to it if you increase the size.Ī cell array is a special type of array (called an "object array" in many other languages) where the "values" are references to other pieces of memory. Because they are all of the same type, your processor can, for example, add a value to all (or many) elements in that array in one step, rather than having to add a value to each number individually (which is much slower). So it could have all (or many) integers of a certain size, or all (or many) floats of a certain size, etc. This is called "vectorization".įurther, modern processors are able to do mathematics on that block of memory very quickly (or at least chunks if it at a time). This allows them to be done in fast C or Fortran libraries rather than slow MATLAB loops.
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There are C/Fortran libraries optimized to do this sort of calculation extremely quickly. Instead, you should switch a struct-of-arrays like Brian L's answer suggests.To be a bit more technical, an array (or rather a matrix), is a single block of memory containing a bunch of equally-sized values of the same data type.This block of memory also has information on the shape of the array, so the multi-dimensional index can be converted to a linear location in the memory block. That includes the field assignment in your question – it is not possible to vectorize that. Kd 32.2 Continuous-time PID controller in parallel form. MATlab file extensions Best Online Courses From Data structure in Touchstone file. You can't do real "vectorized" operations on it because your primitive arrays are all broken up in to separate mxArrays inside each struct element. Key MATLAB commands used in this tutorial are: tf, step, pid, feedback. For example, you can specify row names to include in the table.
Matlab struct full#
So it's better to just do full assignment with the repmat form.īUT: Regardless of how you initialize it, an array-of-structs like this is always going to be inherently slow to work with for larger data sets. T struct2table(S,Name,Value) creates a table from a structure array, S, with additional options specified by one or more Name,Value pair arguments. To be safe, you need to do clear edges before initializing using the indexing syntax. Or if edges is a different type, you could get an error or weird behavior depending on its existing datatype.
Matlab struct code#
If edges has more than 1000 elements, the others will be left unchanged, and your code will be buggy.
Matlab struct update#
There's a problem with the edges(1:1000) form: if edges is already initialized, this syntax will just update the values of selected elements. Note the 1:1000 instead of just 1000 when indexing in to the uninitialized edges array. It is a much better structure for Matlab, and more idiomatic. % NOTE: Only correct if variable is uninitialized!!!Įdges(1:1000) = struct('weight', 1.0) % QUESTIONABLE A struct of arrays ('planar-organized') like Brian's will store each of its fields in primitive arrays which are contiguous in memory, and vectorized (fast) Matlab functions will work on. % Using repmat and full assignmentĮdges = repmat(struct('weight', 1.0), ) The syntax for efficiently initializing an array of structs is one of these. The edges(3) element has 1.0 in its weight like you want the others have. To make this behavior clear, try doing a short array with clear edges edges(1:3) = struct('weight',1.0) and looking at each of edges(1), edges(2), and edges(3). For a nonexistent array, the rest of them get implicitly filled in with structs that have the default value in all their fields. The reason that the structs in your example don't get initialized properly is that the syntax you're using only addresses the very last element in the struct array.