Error in find command....

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

end

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

[shoaib Ch]

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

[Adam Danz]

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).

Answer 1

[Adam Danz]

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

[shoaib Ch]

yup it says dimension mismatches , i think bec of too much values after point , how can i fix uptill one decimal place??

[madhan ravi]

Remember you are dealing with float numbers so add tolerance.

[Adam Danz]

Please provide the full copy-pasted error message and relevant code that produces the error.

[shoaib Ch]

pos_a =  -0.07          0.82             0         -4.03 %values i want to compare

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

as i mention t is array cotaining x values and pos_a is array containing y values at some unknown x values

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

i make a function to show which valve of t gives me value of pos_a (not direct but in approximate) and thanx in advance

[Adam Danz]

There must be a mistake with the code you provided.

1) the first line causes an error because the vector is not enclosed in [brackets].

2) the loop k=1:pos_a, pos_a is a vector, not an integer.

[Adam Danz]

if pos_a(k)>= pos_a(k)+1

How would this ever be true?

[shoaib Ch]

i use if command to check weather it is true or not other wse will go for elese command .... is there be any command in matlab which gives me interval values of t (x axix) on basis of y value , meanx your x value lies with in this intervalval of x??

[Adam Danz]

I understand how the 'if' command works. What I don't understand is what you're trying to do with it. Your statement

if pos_a(k)>= pos_a(k)+1

is analogous to

    if x >= x+1

which would never be the case.

Did you mean to this?

if pos_a(k)>= pos_a(k+1)

Sorry, I don't understand your last question above.

[shoaib Ch]

yup the last ones but it does not gives me the value bec of decimal places as two values are not exectly same , and if you go for greater value it gives you all values that are greater than this

[Adam Danz]

Please provide a minimal working example so I can reproduce your problem.

[shoaib Ch]

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

And and Thanx again for your Kindness

[shoaib Ch]

if these be pos_a values than what be t values ??