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  • How to access a matrix in a matlab struct's field from a mex function?

    - by B. Ruschill
    I'm trying to figure out how to access a matrix that is stored in a field in a matlab structure from a mex function. That's awfully long winded... Let me explain: I have a matlab struct that was defined like the following: matrixStruct = struct('matrix', {4, 4, 4; 5, 5, 5; 6, 6 ,6}) I have a mex function in which I would like to be able to receive a pointer to the first element in the matrix (matrix[0][0], in c terms), but I've been unable to figure out how to do that. I have tried the following: /* Pointer to the first element in the matrix (supposedly)... */ double *ptr = mxGetPr(mxGetField(prhs[0], 0, "matrix"); /* Incrementing the pointer to access all values in the matrix */ for(i = 0; i < 3; i++){ printf("%f\n", *(ptr + (i * 3))); printf("%f\n", *(ptr + 1 + (i * 3))); printf("%f\n", *(ptr + 2 + (i * 3))); } What this ends up printing is the following: 4.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 I have also tried variations of the following, thinking that perhaps it was something wonky with nested function calls, but to no avail: /* Pointer to the first location of the mxArray */ mxArray *fieldValuePtr = mxGetField(prhs[0], 0, "matrix"); /* Get the double pointer to the first location in the matrix */ double *ptr = mxGetPr(fieldValuePtr); /* Same for loop code here as written above */ Does anyone have an idea as to how I can achieve what I'm trying to, or what I am potentially doing wrong? Thanks! Edit: As per yuk's comment, I tried doing similar operations on a struct that has a field called array which is a one-dimensional array of doubles. The struct containing the array is defined as follows: arrayStruct = struct('array', {4.44, 5.55, 6.66}) I tried the following on the arrayStruct from within the mex function: mptr = mxGetPr(mxGetField(prhs[0], 0, "array")); printf("%f\n", *(mptr)); printf("%f\n", *(mptr + 1)); printf("%f\n", *(mptr + 2)); ...but the output followed what was printed earlier: 4.440000 0.000000 0.000000

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  • Is there a better way to declare an empty, typed matrix in MATLAB?

    - by Arthur Ward
    Is there a way to "declare" a variable with a particular user-defined type in MATLAB? zeros() only works for built-in numeric types. The only solution I've come up with involves using repmat() to duplicate a dummy object zero times: arr = repmat(myClass(), [1 0]) Without declaring variables this way, any code which does "arr(end+1) = myClass()" has to include a special case for the default empty matrix which is of type double. Have I missed something a little more sensible?

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  • How to download yahoo historical stock data into xls. format via matlab?

    - by Noob_1
    I have an xls sheet called Tickers (matrix 1 column 500 rows) with yahoo tickers. I want matlab to download the historical data for last 5 years for each stock ticker into a separate xls spreadsheet and save it in a given directory with title of the sheet = ticker. So that means i want a code that will create and save 500 tickers worth of data in 500 separate spreadhseets :) can anyone help or direct?

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  • Why is Matlab Stateflow 7.7 not throwing errors on undefined variables?

    - by Pyrolistical
    Previously in Matlab Stateflow 7.1 all variables and functions had to be included before they can be referred to in the state diagram or else it would throw an error when you tried to parse the diagram. But now in 7.7 it doesn't catch those kinds of errors. Its still compiling the diagram because it catches other syntactic errors. Am I missing an option somewhere? Can this be turned on?

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  • Is it possible to see the underlying implementation of built in functions of matlab?

    - by user198729
    I'm using this example code to grayscale an image,but the result is not right: I = imread('coins.png'); level = graythresh(I); BW = im2bw(I,level); imshow(BW) Where to see how graythresh is actually implemented? BTW,is there a reason for using matlab feels so alike with python? Or is it known that graythresh doesn't work well for images with little spatial resolution(like 62*21 ones)?

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  • Where is my software installed in Linux?

    - by David
    I use whereis matlab and find: /usr/local/bin/matlab , which is a very long bash file. How can I find where matlab is installed, I mean, its installed folder. EDIT: I used the following method: open matlab and use edit svds.m to open the svds.m file and the editor shows the folder:)

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  • What's this setting of MATLAB for(which is causing lots of troubles for lots of people)?

    - by Runner
    This setting in PATH: D:\MATLAB\R2007b\bin\win32 Here is a fresh bad affect by this setting for me: http://stackoverflow.com/questions/2712913/why-does-this-program-require-msvcr80-dll-and-whats-the-best-solution-for-this-k And here's an issue reported by another guy: http://groups.google.com/group/ggobi/browse_thread/thread/dacea0fa93dcaf75 What's that setting for and why it's causing so many problems?

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  • How do i get rid of NaNs in matlab?

    - by Paul
    I have files which have many empty cells which appear as NaNs when i use cell2mat but the problem is when i need to get the average values i cannot work with this as it shows error with NaN. In excel it overlooks, how do i do the same in matlab? thanks

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  • How can I read a textfile into matlab and make it a list?

    - by Ben Fossen
    I have a textfile that has the format gene complement(22995..24539) /gene="ppp" /locus_tag="MRA_0020" CDS complement(22995..24539) /gene="ppp" /locus_tag="MRA_0020" /codon_start=1 /transl_table=11 /product="putative serine/threonine phosphatase Ppp" /protein_id="ABQ71738.1" /db_xref="GI:148503929" gene complement(24628..25095) /locus_tag="MRA_0021" CDS complement(24628..25095) /locus_tag="MRA_0021" /codon_start=1 /transl_table=11 /product="hypothetical protein" /protein_id="ABQ71739.1" /db_xref="GI:148503930" gene complement(25219..26802) /locus_tag="MRA_0022" CDS complement(25219..26802) /locus_tag="MRA_0022" /codon_start=1 /transl_table=11 /product="hypothetical protein" /protein_id="ABQ71740.1" /db_xref="GI:148503931" I would like to read the textfile into Matlab and make a list with the information from the line gene as the starting point for each item in the list. So for this example there will be 3 items in the list. I have tried a few things and cannot get this to work. Anyone have any ideas of what I can do?

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  • Matlab: how do I force ode45 to take steps of exactly 0.01 on the T axis?

    - by Gravitas
    I'm using Matlab to solve a differential equation. I want to force ode45 to take constant steps, so it always increments 0.01 on the T axis while solving the equation. How do I do this? ode45 is consistently taking optimized, random steps, and I can't seem to work out how to make it take consistent, small steps of 0.01. Here is the code: options= odeset('Reltol',0.001,'Stats','on'); %figure(1); %clf; init=[xo yo zo]'; tspan=[to tf]; %tspan = t0:0.01:tf; [T,Y]=ode45(name,tspan,init,options);

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