2d truss analysis

doing trusses for statics class and i keep getting this error when running. triple checked my work i do not have any negative integers

Index in position 1 is invalid. Array

indices must be positive integers or

logical values.

Error in CEE210_CP3_verification (line

70)

PosVec(j,:)=NodeP(EN,:)-NodeP(SN,:);

nNodesP =6 ;

nMembersP =9 ;

NodeP = zeros(nNodesP, 3); %Initialize memory storage

MemberP = zeros(nMembersP, 2);

%.... Input node coordinates

%Member 9 Node 3 to Node 4

NodeP(1,:) = [0,0,0];

NodeP(2,:) = [4,3,0];

NodeP(3,:) = [8,3,0];

NodeP(4,:) = [12,0,0];

NodeP(5,:) = [4,0,0];

NodeP(6,:) = [8,0,0];

MemberS(1,:) = [1,2]; %Member 1 Node 1 to Node 2

MemberS(2,:) = [1,5]; %Member 2 Node 2 to Node 3

MemberS(3,:) = [2,5]; %Member 3 Node 2 to Node 4

MemberS(4,:) = [2,3]; %Member 4 Node 2 to Node 5

MemberS(5,:) = [2,6]; %Member 5 Node 1 to Node 3

MemberS(6,:) = [6,5]; %Member 6 Node 1 to Node 4

MemberS(7,:) = [3,6]; %Member 7 Node 3 to Node 6

MemberS(8,:) = [3,4]; %Member 8 Node 3 to Node 5

MemberS(9,:) = [4,6]; %Member 9 Node 3 to Node 4

PosVecP = zeros(nMembersP, 3); %Initialize memory storage

UnitVecP = zeros(nMembersP, 3);

OppPosVecP = zeros(nMembersP, 3);

OppUnitVecP = zeros(nMembersP,3);

Memberlength=zeros(nMembersP,1);

for (j = 1 : nMembersP)

SN = MemberP(j,1); %SN = start node

EN = MemberP(j,2);

PosVecP(j,:)=NodeP(EN,:)-NodeP(SN,:);

OppPosVecP(j,:) = -PosVecP(j,:);%EN = end node

Memberlength(j,:) = norm(PosVecP(j,:));

UnitVecP(j,:) = PosVecP(j,:)./Memberlength(j,1);

OppUnitVecP(j,:) = -UnitVecP(j,:);

%Finish this section to compute the position vector, length, unit vector,

%and negative unit vector for each member in the truss.

end

%% .Create output for command window

fprintf('%s\n' , '----------------------------------------')

fprintf('%s\n' , '-------------Planar Truss---------------')

fprintf('%s\n' , '----------------------------------------')

for (i = 1 : nNodesP)

fprintf('%s%8i%8.3f%8.3f%8.3f\n',' Node: ',i, NodeP(i,:)')

end

fprintf('\n')

for (i = 1 : nMembersP)

fprintf('%s%8i%8.3f%8.3f%8.3f\n',' Unit Vector: ',i, UnitVecP(i,:)')

end

fprintf('\n\n\n')

%% .Create the plot

fig1 = figure(1); clf; grid on; axis equal; hold on;

xlabel('X'); ylabel('Y'); title('Planar Truss');

for m = 1 : nMembersP

SN = MemberP(m,1);

EN = MemberP(m,2);

X = [NodeP(SN,1); NodeP(EN,1)];

Y = [NodeP(SN,2); NodeP(EN,2)];

Z = [NodeP(SN,3); NodeP(EN,3)];

p = plot(X,Y);

set(p, 'Color', 'k', 'LineWidth', 2);

end % for m, nMembersP

scatter(NodeP(:,1),NodeP(:,2),'fill','red');

Answer 1

[Star Strider]

You don’t have negative integers, however positive integers are integers greater than 0.

Here:

        SN = MemberP(j,1);           %SN = start node
        EN = MemberP(j,2);
        PosVecP(j,:)=NodeP(EN,:)-NodeP(SN,:);

your ‘SN’ and ‘EN’ values are both 0. That is not a valid MATLAB index.

[caroline]

so please how do i change that so its not 0

[Star Strider]

I am not certain what you are doing.

One option could be:

PosVecP(j,:) = NodeP(j,:)-NodeP(j,:);

or perhaps:

PosVecP(j,:) = EN(j,:)-SN(j,:);

I leave it to you to create the matrix you want.