Formatted Output
fprintf Statement
• Syntax:
• You can write formatted output (text) to the
screen or a file using the fprintf command.
fprintf('text and/or format commands', variables)
• This output can include values of various variables
as well as descriptive text.
• The format commands control how the values of the
variables are printed (e.g., significant digits) as well as the
“look” of the output (e.g., tabs and line feeds).
• The text can be printed directly or you can use a
copy-and-paste operation to include the
information in a report.
• The variables can be scalars, vectors, or matrices.
• More than one variable may be printed using the same
fprintf statement.
1
fprintf Statement Continued
fprintf Statement Continued
• Example of line control format commands:
\t
\n
2
• Example, remove the % sign from line 7:
tab command - move to the next tab stop.
new line or line feed command - move to the next line.
fprintf('This is a good test');
• These commands control the “look” and “layout” of most
of the output so that it is readable and understandable.
• These commands appear INSIDE the single quotes.
• Save and run the m.file.
• Now, remove the % sign from line 8:
fprintf('\n\nThis is\t\ta good\n\n test\n\n');
• Other line control commands are available (see help).
• Start a NEW m.file.
– Copy and paste the FIRST starter m.file for this lesson into the
Editor.
– Save it to the H:\ drive, name it as5_3ic.m
3
• Save and run the m.file.
Note the 8 line control
• What is the same?
format commands.
• What is different?
• How would you use these commands to control the “look
and “layout” of the output?
4
• Assume we assigned a value to a scalar variable named
time. We would like to print it to the screen. Remove the
% sign from lines 11 and 12 :
fprintf Statement Continued
time = 12;
• The new line command ( \n ) is useful in adding blank lines
fprintf('Time = ',time);
at the top and bottom of the output as well as in between various
sections of the output.
• Save and run the m.file. Why did it NOT work?
• The new line command ( \n ) is also useful in creating tables
(i.e., vertical lists of data).
• We did not specify where and how to print the value
stored in the variable time.
• Edit the fprintf command (line 12) to:
• The tab command ( \t ) is useful in ensuring that vertical
time = 12;
columns of data “line up” properly, although I prefer to use blank
spaces.
fprintf('\n\nTime = %f \n\n', time);
• Save and run the m.file. What do the \n ’s do?
5
6
fprintf Statement Continued
fprintf Statement Continued
• The %f is an output format command. It tells Matlab
where (right after the = sign) and how (fixed decimal
format) to print the number stored in the variable time.
• All output variable format commands must start with the
% sign (yes, so does the comment operator, and yes this
is confusing). The letter may be different.
• The format command can appear anywhere in between
the single quotes, it does not have to be at the end of the
text. Try (edit line 12 again):
•
Some common “Conversion Specifiers” are:
%e
%E
%f
%g
time = 12;
fprintf('\n\nTime = %f sec. \n\n', time);
• Save and run the m.file.
%G
7
Exponential notation (using lowercase e as in 3.1415e+00)
Exponential notation (using uppercase E as in 3.1415E+00)
Fixed decimal point notation (as in 3.14159)
The more compact of %e or %f , that is Matlab chooses.
Insignificant zeros do not print.
Same as %g, but using an uppercase E.
8
fprintf Statement Continued
fprintf Statement Continued
• Still using line 11:
• We can also control the “width” (the total number of spaces used)
and the “precision” (number of decimal places) to print.
time = 12;
• Remove the % sign from lines 15-19:
• The general format is:
%<flag><width>.<precision><conversion specifier>
fprintf('\nTime = %f sec. \n',time);
• The <flag> controls items such as leading zeros, always printing
the sign (+ or -), etc. See the book or help file.
fprintf('\nTime = %6.3f sec. \n',time);
• The <width> is the total number of spaces to use in printing the
number (including the decimal point).
• The <precision> is the number of decimal places to print.
fprintf('\nTime = %12.3e sec. \n',time);
fprintf('\nTime = %12.3f sec. \n',time);
fprintf('\nTime = %12.3g sec. \n',time);
• The <conversion specifier> was discussed on the
previous page (i.e., e, E, f, g, or G ) .
• Save and run the m.file.
9
• Can we print more than one variable on the same line using
the same fprintf statement? Yes!! Remove the % sign
from lines 22-26:
fprintf Statement Continued
• Did you get?
t = 12;
v = 3.4;
fprintf('\n\n');
fprintf('t = %6.3f sec and v = %3.1f ft/sec',t,v);
fprintf('\n\n');
Time = 12.000000 sec.
Time = 12.000 sec.
Time =
10
12.000 sec.
• Save and run the m.file. Did you get:
Time =
1.200e+001 sec.
Time =
12 sec.
Do the output formats
and the printed output
match?
t = 12.000 sec and v = 3.4 ft/sec
• Notice how the printed output changes when we change
the width, precision, and conversion specifier.
• Also notice where “padding” (extra spaces) appear.
11
• Note that the 1st and 3rd fprintf statements just add the
extra line feeds to give some “extra space.”
• Also, ALL format commands and ALL text must between
the single quotes and the variable names appear at the end.
12
fprintf Statement for Vectors & Matrices
fprintf Statement for Vectors & Matrices
fprintf and for loops combined
• We can leave the data in vector form and use a for
loop to print the table.
• Assume we have the following lists of time
and associated velocities:
• For each “cycle” (iteration) of the for loop we will
print a “t” value and a “v” value on the same line.
t = [0 1 2 3 4 5 6 7]
v = [10 12 14 9 3 -2 -7 -10]
• We will only print one “t” and one “v” value per
line.
• We would like to print a “table” of time and
velocity values.
• Our table should be two vertical columns
and include a title and column headings.
• The desired output is shown on the next page.
13
14
• Start with the “basic table” first.
t = [0 1 2 3 4 5 6 7];
v = [10 12 14 9 3 -2 -7 -10];
for ii=1:1:length(t)
fprintf('\t\t%5.1f\t\t%5.1f\n',t(ii),v(ii));
end
Make sure the format control is "wide"
Remove % signs
enough to print the numbers to the desired
p"precision" and print signs ( + or -), etc.
Time and Velocity for Our Example
Time
sec
---0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Again, let Matlab
figure out how
many values need
to be printed.
Velocity
ft/sec
-------10.0
12.0
14.0
9.0
3.0
-2.0
-7.0
-10.0
• After we initialize the two lists, we will “loop through” all of their
values using the index ii.
• For each cycle of the loop we will print the corresponding t and v
values using the %5.1f format.
• We will “tab over” twice, print a t value, “tab over” twice, print a
v value, then move down one line before the next cycle starts.
15
16
In-Class Problem
• Remove the semicolons and the % signs and run.
• Modify our force-plate m.file so that the program creates
a table of some of the data:
• Save and run the m.file and see what you get.
– Will include the time = 0 values of Fx, Fy and Fz.
• Now we need to add the title and column headers. The
fprintf statements must be BEFORE the for loop.
– Will also include the the values of Fx, Fy and Fz at each 0.1 sec.
– Will also have an “appropriate header” that includes a Title and
Column Headers with Units.
• On your own, enter the following lines before the for
loop, save the m.file and re-run.
• The desired output is shown on the next page
fprintf('\n\n\t\tTime and Velocity for Our Example\n\n')
fprintf('\t\t Time\t
Velocity\n')
fprintf('\t\t sec \t
ft/sec \n')
fprintf('\t\t ----\t
--------\n')
• Everyone should have a completed m.file by the end of
the period.
• The completed m.file will include proper documentation.
Try different combinations of tabs and spaces and see what you get.
17
Force Plate Data for Subject 3 - Jump 2
Time
sec
---0.000
0.100
0.200
0.300
0.400
.
.
.
1.900
2.000
Fx
N
---2
2
8
128
70
.
.
.
23
26
Fy
N
---1
1
12
206
157
.
.
.
1
0
18
Our Plan
Fz
N
---1
1
61
943
979
.
.
.
329
343
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