For-loop instantly jump to largest value

Hi! i have a problem with a for loop. The problem is that the code jumps right to rpm1<9500 instead of doing all the ones above, since all rpm1 values are <9500. Therefore i just get a long vector of zeros. Any ideas on how to fix this?

for i=rpm1;

if rpm1<750;
torque=287.91;
tv1=[tv1 torque];
elseif rpm1<1250;
torque=345,51;
tv1=[tv1 torque];
elseif rpm1<1775;
torque=368,55;
tv1=[tv1 torque];
elseif rpm1<2300;
torque=397,35;
tv1=[tv1 torque];
elseif rpm1<2740;
torque=500,94;
tv1=[tv1 torque];
elseif rpm1<3140;
torque=652,95;
tv1=[tv1 torque];
elseif rpm1<3550;
torque=798,12;
tv1=[tv1 torque];
elseif rpm1<4065;
torque=798,12;
tv1=[tv1 torque];
elseif rpm1<4705;
torque=900;
tv1=[tv1 torque];
elseif rpm1<5325;
torque=884,43;
tv1=[tv1 torque];
elseif rpm1<5860;
torque=855,09;
tv1=[tv1 torque];
elseif rpm1<6340;
torque=808,47;
tv1=[tv1 torque];
elseif rpm1<6865;
torque=763,56
tv1=[tv1 torque];
elseif rpm1<7365;
torque=703,08;
tv1=[tv1 torque];
elseif rpm1<7775;
torque=644,31;
tv1=[tv1 torque];
elseif rpm1<8210;
torque=564,84;
tv1=[tv1 torque];
elseif rpm1<8450;
torque=352,44;
tv1=[tv1 torque];
elseif rpm1<8750;
torque=287,91;
tv1=[tv1 torque];
else rpm1<9500;
torque=0;
tv1=[tv1 torque];
end
end

[Stephen23]

Some points to consider:

• You define a loop with one iteration, and then complain that it has only one iteration.
• You define the loop variable to be i but never use this anywhere, or in anyway increment any variable within the loop.
• You used commas for the decimal radix, which is not supported by MATLAB.
• You apparently generate a vector by concatenating new elements inside the loop. This is inefficient.
• You wrote a huge long list of elseif statements. This is a pointlessly complex way to write code.

Learn to write efficient MATLAB code: put all of the values into one matrix:

M = [...
  0750,287.91;
  1250,345.51;
  1775,368.55;
  2300,397.35;
  2740,500.94;
  3140,652.95;
  3550,798.12;
  4065,798.12;
  4705,900.00;
  5325,884.43;
  5860,855.09;
  6340,808.47;
  6865,763.56
  7365,703.08;
  7775,644.31;
  8210,564.84;
  8450,352.44;
  8750,287.91;
  9500,000.00];

and then learn about such useful functions as interp and bsxfun, and useful operations as logical indexing. Your code will be simpler and much more efficient.

Answer 1

[Andrei Bobrov]

x =      [750       287.91
         1250       345.51
         1775       368.55
         2300       397.35
         2740       500.94
         3140       652.95
         3550       798.12
         4065       798.12
         4705          900
         5325       884.43
         5860       855.09
         6340       808.47
         6865       763.56
         7365       703.08
         7775       644.31
         8210       564.84
         8450       352.44
         8750       287.91
         9500            0];

rpm1 = randi([600 9500],20,1);
out = x(discretize(rpm1,[-inf;x(:,1)]),2)

Answer 2

[Rohan Kale]

Your for loop construct itself is incorrect. It should be

for rpm1 = a:b:c

where a and c are start and end limits and b is increment

Answer 3

[Stephen23]

You do not need such pointlessly complex code using lots of elseif as if MATLAB was an ugly low-level language like C++. Keep your data in matrices or arrays. This should get your started on writing much better code:

>> M = [...
  0750,287.91;
  1250,345.51;
  1775,368.55;
  2300,397.35;
  2740,500.94;
  3140,652.95;
  3550,798.12;
  4065,798.12;
  4705,900.00;
  5325,884.43;
  5860,855.09;
  6340,808.47;
  6865,763.56
  7365,703.08;
  7775,644.31;
  8210,564.84;
  8450,352.44;
  8750,287.91;
  9500,000.00];
>> vec = 1000:500:9000; % points you want to find values for
>> out = interp1(M(:,1),M(:,2),vec(:))
out =
     316.71
     356.48
     380.89
     444.44
     599.75
     780.42
     798.12
     867.37
     892.59
     874.83
     841.49
     794.78
     747.23
     683.73
      603.2
     341.69
     191.94

Answer 4

[Image Analyst]

When you set the loop iterator, i, equal to a vector rpm1, the iterator, i, takes on all the values in the vector, rpm1. So you need to check i, not rpm1, like this:

for i=rpm1
  if i < 750
      torque = 287.91;
      tv1 = [tv1 torque];
  elseif i < 1250
      torque = 345,51;
      tv1 = [tv1 torque];

By the way, you don't use semicolons at the end of ifs, elseifs, or ends.

[Image Analyst]

Or you could do

for i = length(rpm1)
  if rpm1(i) < 750;
      torque=287.91;
      tv1=[tv1 torque];
  elseif rpm1(i) < 1250;
      torque=345,51;
      tv1=[tv1 torque];

where you're adding an index to rpm1.

[Stephen23]

for i = length(rpm1)

??? Surely:

for i = 1:length(rpm1)

[Image Analyst]

Of course, sorry - good catch, thanks.