Error in find command....

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shoaib Ch 2019-3-14

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/450131-error-in-find-command

编辑： shoaib Ch 2019-4-2

t=linspace(xq(1),xq(np),1001)

y2=polyval(pmon,t)

plot(t,y2,'k--',x)

for j=1:6

for i=1:1001;

t1(j)=find(y2(i)=pmon(j))

end

i want to find value of t(x axis) for which value of pmon(y axis) is given ??

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shoaib Ch 2019-3-14

it is not giving me value for t , i want to use it for finding roots

Adam Danz 2019-3-14

Have you implemented the correction suggested in the answers section below?

If you've implemented that correction and 't' is empty, that means there were no matches between y2(i) and pmon(i).

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回答（1 个）

Adam Danz 2019-3-14

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/450131-error-in-find-command#answer_365428

在 MATLAB Online 中打开

One equal sign assigns a value to a variable.

Two equal signs perfoms a comparison between A and B and returns a logical value.

t1(j) = find(y2(i) = pmon(j))    %incorrect
t1(j) = find(y2(i) == pmon(j))   %correct

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shoaib Ch 2019-3-15

在 MATLAB Online 中打开

xq=[ -3, -2, -1, 2, 6, 7];
yq=[ 1, -2, 1, -2, 2, -2];
pmon=[-61/840, 49/60, -1663/840, -1693/420, 169/15, 73/7]; %interpolation values
t=linspace(xq(1),xq(6),1001) %values of xq
y2=polyval(pmon,t)
plot(t,y2,'k--') 

Now i want to chect weather there exist a root between pmon values ,next program give me root values

for i=1:5;
    if pmon(i)<0 & pmon(i+1)>0
pos_a(i)=pmon(i)
    elseif pmon(i)>0 & pmon(i+1)<0
pos_a(i)=pmon(i)
        else
    end

now , pos_a is values of y axis and i want to find what be the values of t (x values) which give me these y values according to data ... for this i use that code but its not working

for i=1:5;
 if pos_a(i)>= pos_a(i+1)
     s0=t(pos_a(i))% ..statements to get the root in t(pos a(i)) to t(pos a(i+1))
     s1=t(pos_a(i+1))
    else
        s1=t(pos_a(i)) % ..statements to get the root in t(pos a(i)) to t(pos a(i+1))
        s0=t(pos_a(i+1))
    end
end