How do I apply an if statement to every row of a matrix of varying number of rows?

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Shannon
Shannon 2013-10-30
评论： sixwwwwww 2013-10-30
I'm trying to write within an if statement for the program load a matrix from a text file. The first column of the matrix are m values, the second are c values, and the third are k values. The program needs to see if m, c, and k are greater than zero. If they're not, it outputs an error message, an if they are, then it uses those numbers to do some other calculations, and then it needs to see if each available value of R, a number calculated by the program, is less than, equal to, or greater than 1.
I've got it working if I specifically type into the program which row of R to look at, but I don't know how to make it automatically run through each row of R.
Please help!
Here's the code I have when the row numbers are included in the program:
if true
A=load('Dynamics.txt');
m=A(:,1);
c=A(:,2);
k=A(:,3);
p=c./m;
q=k./m;
Wn=q.^(1/2);
R=p./(2.*Wn);
Wd=Wn.*(1-(p.^2)).^0.5;
if (m(1,1)>0)&&(c(1,1)>0)&&(k(1,1)>0)
if R(1,1)>1
fprintf('1) Natural frequency= %1.3g rad/s; Damping ratio=%1.3g; System is overdamped, damped frequency does not exist.\n', Wn(1,1), R(1,1))
elseif R(1,1)==1
fprinf('1) Natural frequency= %1.3g rad/s; Damping ratio=%1.3g; System is critically damped, damped frequency does not exist.\n', Wn(1,1), R(1,1))
elseif R(1,1)<1
fprintf('1) Natural frequency=%1.3g rad/s; Damping ratio=%1.3g; Damped frequency=%1.3g rad/s; System is underdamped.\n', Wn(1,1), R(1,1), Wd(1,1))
end
else disp '1) Error in input values.'
end
end
Any help I can get would be super appreciated!!

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回答（1 个）

sixwwwwww
sixwwwwww 2013-10-30
Dear Shannon, you can put the if-else statements in a loop as follows:
A=load('Dynamics.txt');
m=A(:,1);
c=A(:,2);
k=A(:,3);
p=c./m;
q=k./m;
Wn=q.^(1/2);
R=p./(2.*Wn);
Wd=Wn.*(1-(p.^2)).^0.5;
for x = 1:numel(R)
if (m(x)>0)&&(c(x)>0)&&(k(x)>0)
if R(x)>1
fprintf('1) Natural frequency= %1.3g rad/s; Damping ratio=%1.3g; System is overdamped, damped frequency does not exist.\n', Wn(x), R(x))
elseif R(x)==1
fprinf('1) Natural frequency= %1.3g rad/s; Damping ratio=%1.3g; System is critically damped, damped frequency does not exist.\n', Wn(x), R(x))
elseif R(x)<1
fprintf('1) Natural frequency=%1.3g rad/s; Damping ratio=%1.3g; Damped frequency=%1.3g rad/s; System is underdamped.\n', Wn(x), R(x), Wd(x))
end
else
disp '1) Error in input values.'
end
end
I hope it is what you need. Good luck!
  2 个评论
Shannon
Shannon 2013-10-30
Thank you so much! I also found another way. It might be a little messier, but it got me what I needed:
if true
A=load('Dynamics.txt');
m=A(:,1);
c=A(:,2);
k=A(:,3);
p=c./m;
q=k./m;
Wn=q.^(1/2);
R=p./(2.*Wn);
Wd=Wn.*(1-(R.^2)).^0.5;
x=size(R,1);
for s=1:x
if (m(s,1)>0)&&(c(s,1)>0)&&(k(s,1)>0)
if R(s,1)>1
fprintf('%1g. Natural frequency=%1.3g rad/s; Damping ratio=%1.3g; System is overdamped, damped frequency does not exist. \n', s, Wn(s,1), R(s,1))
elseif R(s,1)==1
fprintf('%1g. Natural frequency=%1.3g rad/s; Damping ratio=%1.3g; System is critically damped, damped frequency does not exist. \n', s, Wn(s,1), R(s,1))
elseif R(s,1)<1
fprintf('%1g. Natural frequency=%1.3g rad/s; Damping ratio=%1.3g; Damped frequency=%1.3g rad/s; System is underdamped.\n',s, Wn(s,1), R(s,1), Wd(s,1))
end
else
fprintf('%1g. Error in inputted values.\n', s)
end
end
end

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