logical operators problem T_T

Hi,

I am new to Matlab and still trying to understand its usage. I'm trying to read data from a .dat file and solve simple mathematical problem. When I tried to enter one sample data it came out right, but once I tried 2 rows of data, this message occurred. Please help me.

The error ??? Operands to the and && operators must be convertible to logical scalar values.

Error in ==> magnitude at 14
    if wm>0.1 && wm<=9.5;

my .m file is like this. Thank you for your help :)

% This file tries to sort all data and changes all magnitude to bodywave
% magnitude
historicalinput = load('hiseq.dat');
% Arrangement of data = year, lat, long, depth, rm, sm, bm, wm
year = historicalinput (:,1);
lat = historicalinput (:,2);
long = historicalinput (:,3);
depth = historicalinput (:,4);
rm = historicalinput (:,5);
sm = historicalinput (:,6);
bm = historicalinput (:,7);
wm = historicalinput (:,8);
% Calculation of each magnitude
  if wm>0.1 && wm<=9.5;
  wm = wm
% change rm to wm
  elseif rm>0.1 && rm<9.5;
  wm = 0.690*rm+1.7738
% change sm to wm
  elseif sm>0.1 && sm <9.5;
  wm = 1.2765*sm-1.0825
%change bm to wm
  else bm>0.1 && bm<9.5;
  wm = 0.7813*bm+1.6562
  end

% print all data in new .dat file
Filename = 'results';
FID = fopen (Filename, 'w');
if FID < 0, error('Cannot open file'); end
data = [year', lat', long', depth', rm', sm', bm', wm'];
fprintf(FID, '%g %g %g %g %g %g %g %g %g¥n', data');
fclose(FID)

[mastura azmi]

ok, I forgot,

my input data was

1973 4.4 96.33 33 0 0 4.4 0

1975 9.3 89.05 46 3.1 0 0 0

Answer 1

[Jan]

The error message means, that wm is not a scalar, but && needs scalar logical arguments.

Do you want

if any(wm>0.1 && wm<=9.5)

or

if all(wm>0.1 && wm<=9.5)

?

[mastura azmi]

I got confused here. wm is scalar, if I change only keeping to wm<=9.5, there result came out nicely.

Why this happen?

[Image Analyst]

How is wm a scalar when you say this:

wm = historicalinput (:,8);

The colon means "all rows" so if historicalinput is a 2D array, wm is a column vector, taken from the 8th column of historicalinput.

[Jan]

"if wm<=9.5" performs implicitely a "if all(wm<=9.5) && ~isempty(wm)". This automatic conversion is hard to debug and therefore it is a good programming practize to avoid non-scalar IF and WHILE expressions.