error in eval command

Question

Mudasir Ahmed 2014-10-1

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/156934-error-in-eval-command

评论： Mudasir Ahmed 2014-10-1

采纳的回答： Thorsten

clear all clc

a=[12 2 10 20 1 20]; b=[5 21 4 1 4 5]; c=[23 18 13 10 13 17]; d=[8 3 14 6 19 1];

for x=1:6 eval(sprintf('ch%d=[a(1,x) b(1,x) c(1,x) d(1,x)]',x)); end

for y=1:6 eval(sprintf('obj%d=[ch%d(1,1)+(2*ch%d(1,2))+(3*ch%d(1,3))+(4*ch%d(1,4))-30]',y)); end

output of first loop (correct response) ch1 = 12 5 23 8 ch2 = 2 21 18 3 ch3 = 10 4 13 14 ch4 = 20 1 10 6 ch5 = 1 4 13 19 ch6 = 20 5 17 1

in above program, matlab execute and return correct response of first loop, but give error in second loop (Error: This statement is incomplete. ) i want to execute following instruction using eval function for all ch1ch2.....ch6 variables, e.g ch1=[12 5 23 8] a=12 b=5 c=23 d=8 obj=a+2b+3c+4d-30

kindly help me. thanx in advance

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Oleg Komarov 2014-10-1

编辑：Oleg Komarov 2014-10-1

Just do NOT use eval(). You are building a nightmare for yourself as the example code proves.

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Answer 1

Thorsten 2014-10-1

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https://ww2.mathworks.cn/matlabcentral/answers/156934-error-in-eval-command#answer_153467

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for y=1:6 
  eval(sprintf('obj%d=[ch%d(1,1)+(2*ch%d(1,2))+(3*ch%d(1,3))+(4*ch%d(1,4))-30]',[y y y y y]));
end

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Mudasir Ahmed 2014-10-1

thanx sir, its working :) sir can u defined why you have used [y y y y y]. i got it little bit, i think as equation contain 5 terms a+2b+3c+4c-30 thts why u have used a matrix of 5 y. kindly explain it logically , thanx again sir

Mudasir Ahmed 2014-10-1

i got it sir. in eval command %d sign is 5 times used, that's why we have to make a matrix of 5 y.

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Answer 2

Michael Haderlein 2014-10-1

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/156934-error-in-eval-command#answer_153471

在 MATLAB Online 中打开

100 % agree with Oleg. Do not use these statements: http://www.mathworks.com/matlabcentral/answers/57445-faq-how-can-i-create-variables-a1-a2-a10-in-a-loop

To archieve this obj array, you can do the following:

a=[12 2 10 20 1 20]; b=[5 21 4 1 4 5]; c=[23 18 13 10 13 17]; d=[8 3 14 6 19 1];
ch=cat(1,a,b,c,d)';
obj=ch*(1:4)'-30;

Alternatively, you define a,b,c,d as column vectors and concatenate along the second dimension without transposing. In any case, this is the way you should do it in Matlab.