Matrix dimensions must agree.

I am using an array value

FPR = [1.0:0.001:2.0];          
n = length(FPR);

to give values into a for loop

for i = [1:1:n]
    FPR(i) = (i);

in the for loop i use an if statement to interpolate an answer from a graph and it uses an array. I know that T03 and CombTD have become vectors but i dont know how to get my if statement to work for vectors and not elements. This is the code.

a = [300,400,500,600,700,800,900];

TempInlet = T03;
TempDiff = CombTD;

LSearch = find(a <= TempInlet,1,'last');
HSearch = find(a >= TempInlet,1,'first');
lower  = a(LSearch);
higher = a(HSearch);
if lower>=300 && higher<=400
    xlower = TempDiff/37076.92308;
    yhigher = TempDiff/36230.76923;
elseif lower>=400 && higher<=500
    xlower = TempDiff/36230.76923;
    yhigher = TempDiff/35461.538461;
elseif lower>=500 && higher<=600
    xlower = TempDiff/35461.538461;
    yhigher = TempDiff/34615.384615;
elseif lower>=600 && higher<=700
    xlower = TempDiff/34615.384615;
    yhigher = TempDiff/33769.230769;
elseif lower>=700 && higher<=800
    xlower = TempDiff/33769.230769;
    yhigher = TempDiff/33230.76923;
elseif lower>=800 && higher<=900
    xlower = TempDiff/33230.76923;
    yhigher = TempDiff/32769.230769;
end

percentage = (TempInlet-lower)/100;

FAR = xlower+((yhigher-xlower)*percentage)

and this is the error code

Matrix dimensions must agree.

Error in Looptest (line 100)
LSearch = find(a <= TempInlet,1,'last');

[KSSV]

Give either dimensions or values of the variables......so that we can run the code...

Answer 1

[N.]

The error is in these lines:

 LSearch = find(a <= TempInlet,1,'last');
 HSearch = find(a >= TempInlet,1,'first');

if a and TempInlet have not the same size, you cannot compare them. What do you want to do exactly ? What is "lower" and "higher" ?

Answer 2

[Walter Roberson]

For vector TempInlet, you can replace

LSearch = find(a <= TempInlet,1,'last');
HSearch = find(a >= TempInlet,1,'first');

with

[~, LSearch] = histc(TempInlet, [a, inf]);
HSearch = LSearch;
mask = TempInlet ~= a(LSearch);
HSearch(mask) = HSearch(mask) + 1;

The mask will usually be true: it will only be false in the places where the temperatures are exactly on the boundary.

This is a translation of your code. However, I do not think you need HSearch or xlower or xupper and all those if statements. I think you should use just a small number of lines:

 temp_divs = [37076.92308, 36230.76923, 35461.538461, 34615.384615, 33769.230769, 33230.76923, 32769.230769];

xlower = TempDiff ./ temp_divs(LSearch);
xupper = TempDiff ./ temp_divs(LSearch+1);