Array indices must be positive integers or logical values MATLAB error

2020 5 10
1 个回答
更新时间：2020 5 10
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Why do I keep getting an error "Array indices must be positive integers or logical values"?
m1=100; m2=50; k1=7410; k2=8230; b1=1430; b2=153;
A=[0 1 0 0;
-(k1+k2)/m1 -(b1+b2)/m1 k2/m1 b2/m1;
0 0 0 1;
k2/m2 b2/m2 -k2/m2 -b2/m2];
B=[0 0;
k1/m1 b1/m1
0 0;
0 0];
C=[1 0 0 0;
0 0 1 0;
k1/m1 b1/m1 0 0;
-k2/m2 -b2/m2 k2/m2 b2/m2];
D=[0 0;
0 0
k1/m1 b1/m1
0 0];
h0=0.05;
t0=1;
w=2*pi/t0;
t=0:0.01:4;
z0=h0*sin(w*t).*(0<=t & t<t0)
z0dot=h0*w*cos(w*t).*(0<=t & t<t0);
sys=ss(A,B,C,D);
lsim(sys,z0(t),t)

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回答（1 个）

Toder
Toder 2020-5-10

0 个投票

z0(t) is causing the error. t is a vector of decimals, and you cannot use a decimal as an index. Indices must be positive integers, or logical values, as the error mentions.

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Ok great thank you. I now get an error that my input U must be a matrix with as many rows as samples in my time vector T, and as many colums as input channels.
My z0 is a 1x401 double, t is a 1x401 double so there wouldn't be a problem here right?
I'm confused at to what it means "as many columns as input channels". Am I supposed to use the repmat command possibly?
Walter Roberson
Walter Roberson 2020-5-10
My z0 is a 1x401 double
No, your sys has 2 inputs and 4 outputs, and 401 time points, so your z0 should be 401 x 2 . You should not be replmat() your existing z0: you should be defining pairs of inputs that you want the output state to be calculated for.
Ok thank you. So what I could thereotically do is for my input for the lsim use [z0;z0dot] then? You also mention z0 should be a 401 x 2, why is that instead of a 2 x 401?

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