I have a finite diference problem in structured grid in PETSc, and DM context helps me to create the matrix really easy, DM give me a whole matrix of rectangular domain that is good to me because I'm using this reference system, but I have an irregular shape in my problem, it means that I'm not using a lot of entries in this matrix. How can I do to don't allocate this space in the matrix assembling and tell KSP context not to use this entries to solve the problem?
My code is something like this:
DMDACreate2d()
DMCreateMatrix()
DMDAGetCorners()
! loop along the local matrix
DO i,1,width_y
DO i,1,width_y
IF (IsInsideProblemDomian) THEN
SetMatStencil()
MatSetValuesStencil()
END IF
END DO
END DO
MatAssemblyBegin()
MatAssemblyBegin()
Related
As an OpenCASCADE newbie, I am reading the OpenCASCADE tutorial:
https://www.opencascade.com/doc/occt-7.4.0/overview/html/occt__tutorial.html
There are following two curious calls:
BRepLib::BuildCurves3d(threadingWire1);
BRepLib::BuildCurves3d(threadingWire2);
The tutorial explains the need for these two calls in this way:
Remember that these wires were built out of a surface and 2D curves. One important data item is missing as far as these wires are concerned: there is no information on the 3D curves. Fortunately, you do not need to compute this yourself, which can be a difficult task since the mathematics can be quite complex. When a shape contains all the necessary information except 3D curves, Open CASCADE Technology provides a tool to build them automatically. In the BRepLib tool package, you can use the BuildCurves3d method to compute 3D curves for all the edges of a shape.
which I did not find entirely clear.
Imagine that I have constructed some TopoDS_Shape object.
How can I, in general, figure out whether BRepLib::BuildCurves3d call is necessary or not?
With this code you can get the 3D curve of an edge (take from BRepExtrema_DistanceSS.cxx):
Standard_Real aFirst, aLast;
Handle(Geom_Curve) pCurv = BRep_Tool::Curve(E, aFirst, aLast);
If you have not created the 3D curves, pCurv will be a null handle. Using it will result in segmentation faults.
I have been excited about where the 3D curves are actually used. Therefore I have tried several algorithms. These are the algorithms I have tried where the 3D curves are not used:
Visualizing
Export to BREP
Export to STEP
Length Measurement
Checking Whether a Wire Is Closed or Ordered
The only algorithm I have found where the 3D curves are used are extrema/distance computations with BRepExtrema_DistShapeShape. You will not be able to use this class if you have not created the 3D curves.
I'm looking for an elegant way of useing ndgrid and interpn in a more "general" way - basically for any given size of input and not treat each rank in a separate case.
Given an N-D source data with matching N-D mesh given in a cell-array of 1D vectors for each coordinate Mesh={[x1]; [x2]; ...; [xn]} and the query/output coordinates given in the same way (QueryMesh), how do I generate the ndgrid matrices and use them in the interpn without setting a case for each dimension?
Also, if there is a better way the define the mesh - I am more than willing to change.
Here's a pretty obvious, conceptual (and NOT WORKING) schematic of what I want to get, if it wasn't clear
Mesh={linspace(0,1,10); linspace(0,4,20); ... linsapce(0,10,15)};
QueryMesh={linspace(0,1,20); linspace(0,4,40); ... linsapce(0,10,30)};
Data=... (whatever)
NewData=InterpolateGeneric(Mesh,QueryMesh,Data);
function NewData=InterpolateGeneric(Mesh,QueryMesh,Data)
InGrid=ndgrid(Mesh{:});
OutGrid=ndgrid(QueryMesh{:});
NewData=interpn(InGrid{:},Data,OutGrid{:},'linear',0.0)
end
I think what you are looking for is how to get multiple outputs from this line:
OutGrid = ndgrid(QueryMesh{:});
Since ndgrid produces as many output arrays as input arrays it receives, you can create an empty cell array in this way:
OutGrid = cell(size(QueryMesh));
Next, prove each of the elements of OutGrid as an output argument:
[OutGrid{:}] = ndgrid(QueryMesh{:});
I am creating a Sudoku project in vb.net, to such an end I need to store a list of all the possibilities for each square where the squares are indexed by one number. for example the computer needs to know that for square [8] the numbers {1,3,5,9} are possible etc... I began by using a jagged array however there is no apparent 'remove' method which needs to be called a lot. this makes my code looks ugly with all the redim statements in it and so I was curious as to whether a list or arraylist would be best suited to my purposes? I have discovered arraylists have a remove method but I have also read that array lists are all but deprecated and i want to know if there is a nicer solution to this.
I am working on a basic graph implementation(Adj List based) in C so that I can re-use the basic structure to solve all graph related problems.
To map a graph I draw on a paper,I want the best and easiest way.
Talking of the way I take the input rather then how should I go about implementing it! :)
Should I make an input routine which asks for all the nodes label first and then asks for what all edges are to be connected based on two labels?
What could be a good and quick way out? I want an easy way out which lets me spend less amount of energy on the "Input".
Best is to go for input of an edge list,
that is triplets of,
Source, Destination, Cost
This routine can be used to fill Adj List and Adj Matrix.
With the latter, you would need to properly initialize the Matrix though and setup a convention to determine non existent edges.
Here you find details about representation of graph:
Graph-internal-representaion
However here some codes in c++ and java are also given,which you can easily convert to C codes.
I have to make an application that recognizes inside an black and white image a piece of tetris given by the user. I read the image to analyze into an array.
How can I do something like this using C?
Assuming that you already loaded the images into arrays, what about using regular expressions?
You don't need exact shape matching but approximately, so why not give it a try!
Edit: I downloaded your doc file. You must identify a random pattern among random figures on a 2D array so regex isn't suitable for this problem, lets say that's the bad news. The good news is that your homework is not exactly image processing, and it's much easier.
It's your homework so I won't create the code for you but I can give you directions.
You need a routine that can create a new piece from the original pattern/piece rotated. (note: with piece I mean the 4x4 square - all the cells of it)
You need a routine that checks if a piece matches an area from the 2D image at position x,y - the matching area would have corners (x-2, y-2, x+1, y+1).
You search by checking every image position (x,y) for a match.
Since you must use parallelism you can create 4 threads and assign to each thread a different rotation to search.
You might not want to implement that from scratch (unless required, of course) ... I'd recommend looking for a suitable library. I've heard that OpenCV is good, but never done any work with machine vision myself so I haven't tested it.
Search for connected components (i.e. using depth-first search; you might want to avoid recursion if efficiency is an issue; use your own stack instead). The largest connected component should be your tetris piece. You can then further analyze it (using the shape, the size or some kind of border description)
Looking at the shapes given for tetris pieces in Wikipedia, called "I,J,L,O,S,T,Z", it seems that the ratios of the sides of the bounding box (easy to find given a binary image and C) reveal whether you have I (4:1) or O (1:1); the other shapes are 2:3.
To detect which of the remaining shapes you have (J,L,S,T, or Z), it looks like you could collect the length and position of the shape's edges that fall on the bounding box's edges. Thus, T would show 3 and 1 along the 3-sides, and 1 and 1 along the 2 sides. Keeping track of the positions helps distinguish J from L, S from Z.