how to find almost equal entries in 2 row vectors?

delta =

Columns 1 through 7

   -5.0000   -4.5000   -4.0000   -3.5000   -3.0000   -2.5000   -2.0000

Columns 8 through 14

   -1.5000   -1.0000   -0.5000         0    0.5000    1.0000    1.5000

Columns 15 through 21

    2.0000    2.5000    3.0000    3.5000    4.0000    4.5000    5.0000

p42 =

Columns 1 through 7

   74.9106   72.4174   69.9589   67.5351   65.1461   62.7918   61.7295

Columns 8 through 14

   59.6842   57.6910   55.7487   53.8564   52.0129   50.2170   48.4677

Columns 15 through 21

   46.7635   45.1032   43.4854   41.9085   40.3710   38.8713   37.4077

p43 =

Columns 1 through 7

   31.9658   33.2883   34.6411   36.0260   37.4448   38.8993   40.3911

Columns 8 through 14

   41.9217   43.4927   45.1054   46.7612   48.4613   50.2070   51.9995

Columns 15 through 21

   53.8397   55.7288   57.6678   59.6575   60.7376   63.0215   65.3396

p42 and p43 are calculated from delta.. i need to find that value of delta for which p42 and p43 are exactly or almost equal i need a way to find (by interpolating) the almost exact value which these two vectors have in common. i suppose i could use polyfit to get two polynomials that fit these vectors but i dont know how to use polyfit in this case since that needs two data vectors. and even if i could use polyfit i have no idea where to go from there. help

[the cyclist]

In the example you have given, what do you want the output to be?

[Qasim Manzoor]

i updated the original query. i actually want to find that value of delta for which p42 and p43 are exactly equal. delta is like x, and p42 and p43 are functions of x...

Answer 1

[dpb]

Just one line for brevity, same works for entire altho size of outputs grows. Might want to select overlapping subsections via min/max of the two vectors combined to limit the problem space if the vectors are large...

>> p42=[46.7635   45.1032   43.4854   41.9085   40.3710   38.8713   37.4077];
>> p43=[41.9217   43.4927   45.1054   46.7612   48.4613   50.2070   51.9995];
>> [k,d]=dsearchn(p42',p43');
>> [md,ix]=min(d);
>> [p42(k(ix)) p43(ix) md]
ans =
 45.1032   45.1054    0.0022
>>

[Qasim Manzoor]

i updated the original query. i actually want to find that value of delta for which p42 and p43 are exactly equal. delta is like x, and p42 and p43 are functions of x. and i need to find the value of delta when p42 and p43 are both equal

[dpb]

If there are two identical values in the two vectors the returned value from the above will be zero.

Unless the two vectors are computed precisely identically, from fp operations there may not be any exact equality.

But, if the idea is for exact equality then the result would most easily be from

find(ismember(P42,P43))

[Qasim Manzoor]

the idea was for getting an almost equal value. but i came up with another solution. x1=polyfit(delta,p42,3) x2=polyfit(delta,p43,3) roots(x2-x1)

now im getting three roots one from which i just need the real one nd neglect complex ones ans =

   2.3466 +44.7738i
   2.3466 -44.7738i
   0.9976  
any idea how i can do this?

[dpb]

Oh, that's a different problem than I thought you meant--

>> interp1([p42-p43]',delta',0)
ans =
  1.0014
>>

Or, use fsolve and the generator to solve directly

[Qasim Manzoor]

thank you very much for the interp1 tip ,its perfect. p.s i dont know how to use fsolve(matlab noob)

[dpb]

The general idea is --

Write a function (m-file) that describes the problem--

function F = myfun(x)
  F = P42func(x)-P43func(x);

Save this function file as myfun.m somewhere on your MATLAB path.

Next, set up an initial point and options and call fsolve:

x0 = 0;  % Make a starting guess at the solution
options = optimset('Display','off');  % Turn off display
[x,Fval,exitflag] = fsolve(@myfun,x0,options);

More details, see

doc fsolve

Answer 2

[dpb]

Oh, that's a different problem than I thought you meant--

>> interp1([p42-p43]',delta',0)
ans =
1.0014
>>

Or, use fsolve and the generator to solve directly