MATLAB: Updating a zeroized matrix with provided row vectors

for loopMATLABmatrix

So I'm not sure if this can be done, but this is what I'm trying to do. I have a matrix (Force) that I've initialized to zero, it will always have three columns, but the rows will vary based on the nnd variable (determined by user input). Also based on user input is the Nodal Loads matrix, where Column 1 is the node number and column 2:4 are nodal loads. As you can see, there are nodes missing in the user input, meaning that if the user didn't input a value, then that nodal row remains zero. Is there a way to take the user input for Nodal_Loads and update the information into the Force matrix? My desired endstate is shown below. Thanks for the help.

Nodal_Loads = [2 0 -1000 0] %example 1

or

Nodal_Loads = [1 0 0 40; 3 -1000 0 40; 4 0 2000 40; 5 0 0 40; 8 1000 -2000 40; 9 0 0 40] %example 2

nnd = 9 %can be any number based on user input (I'll just say 9 for this example)

Force = zeros(nnd,3)

(Desired Endstate) %example 2

Force matrix now looks like:

Force = [0 0 40; 0 0 0; -1000 0 40; 0 2000 40; 0 0 40; 0 0 0; 0 0 0; 1000 -2000 40; 0 0 40]

Best Answer

 Force(Nodal_Loads(:,1),:) = Nodal_Loads(:,2:4)

Related Solutions

MATLAB: Is it possible to apply load on nodes

Hello Mohammadmahdi,

Sorry for the delay. I have shown below an example that should guide you to model your problem. This is a classical moving load problem. Instead of applying loads on nodes, I have used a function that applies pressure at different location on the bridge as people/load travel with time. The load can be much complicated distribution, here I am assuming it is a uniformly distributed over a short span that represents typical stride of walking.

The loading function is movingPulseFcn. Put the code below in a MATLAB file and execute. Note that I have plotted displacement using a for loop which has a pause, it will wait for you to look at the result, press any key to continue to next time step.

model = createpde('structural','transient-solid');
gm=multicuboid(10,4,0.3);
model.Geometry = gm;
E = 210E9; nu = 0.3; rho = 8000; 
structuralProperties(model,'YoungsModulus',E, ... 
    'PoissonsRatio',nu, ... 
    'MassDensity',rho);
structuralBC(model,'Face',[5 3],'XDisplacement',0,'YDisplacement',0,'ZDisplacement',0);
generateMesh(model);
structuralBoundaryLoad(model,'Face',2,'Pressure',@movingPulseFcn);
d0=[0,0,0];
v0=[0,0,0];
structuralIC(model,'Displacement',d0,'Velocity',v0);
t_max = 20;
tlist=0:0.1:t_max; 
structuralResults=solve(model,tlist);
for i = 1:numel(structuralResults.SolutionTimes)
    pdeplot3D(model,'ColorMapData',structuralResults.Displacement.uz(:,i))
    title(['Deflection of bridge at Time = ' num2str(structuralResults.SolutionTimes(i))]);
    pause
end
function P = movingPulseFcn(region,state)
x = region.x+5; % Make the left end x = 0
dx = 0.4; % Approximate half stride. Stride is 2*dx = 0.8 (m)
%Distribute the load over an area:
A = 0.8*4;
P = zeros(1,numel(x));
loadVelocity = 1.5; %m/sec
if isnan(state.time)
    P = nan(1,numel(x));
end
if state.time < 7 % Load would cross the bridge in about 7 sec
    loadLocation = loadVelocity*state.time;
    x1 = loadLocation-dx;
    x2 = loadLocation+dx;
      idx = x>x1 & x<x2;
      % Weight of four people
      F = 2000;
      P(idx) = 2000/A;
  end
end

MATLAB: Index Exceeds Matrix Dimensions

Due to the absence of comments, we cannot guess the intention of the code. You do not provide the files "rightlist2.txt" and "leftlist2.txt", such that we cannot run your code. Without knowing, what you want to achieve an the possibility to run the code, there is no chance to guess the cause of the problem.

So all I cann suggest is using the debugger:

dbstop if error

Now Matlab stops when the error occurs. Then check the current values:

size(X)
size(nodes2)
elements2(i,1)
elements2(i,2)
elements2(i,3)

By the way, this looks nicer:

X(:,:,i) = [1, nodes2(elements2(i,1),1:2); ...
            1, nodes2(elements2(i,2),1:2);
            1, nodes2(elements2(i,3),1:3)];

And when I see this leaner formulation, I think the 3rd line requests the 3rd column of nodes2, which has 2 columns only?! Perhaps it should be "1:2" also.

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