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ch-05-ex-04-solution.cpp
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R1106 Programming Concept Rouaze
ch-05-ex-04-solution.cpp
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/*
* chapter-05-exercise-04.cpp
*
* Standard deviation of array
* Input the array as extra command line arguments:
* ./ch-05-ex-04-solution 5.0 4.8 5.3 2.9
*
* Created on: Oct 8, 2012
* Author: Radu Popescu <radu.popescu@epfl.ch>
*/
#include <cstdlib>
#include <cmath>
#include <iostream>
void
mean_and_std
(
const
double
*
const
v
,
const
double
size
,
double
&
mean
,
double
&
stdev
)
{
mean
=
0.0
;
for
(
int
i
=
0
;
i
<
size
;
++
i
)
{
mean
+=
v
[
i
];
}
mean
/=
size
;
double
s1
=
0.0
;
for
(
int
i
=
0
;
i
<
size
;
++
i
)
{
s1
+=
std
::
pow
(
v
[
i
]
-
mean
,
2
);
}
stdev
=
std
::
sqrt
(
s1
/
(
size
-
1
));
}
/*
* This function computes the mean and standard deviation of a series
* of floating point numbers using a recurrence relation.
* This is useful for continuous processes and is resistant to round-off
* error.
*
* Attributed to B.P. Welford, Technometrics, 4,(1962), 419-420.
*/
void
mean_and_std_rec
(
const
double
*
const
v
,
const
double
size
,
double
&
mean
,
double
&
stdev
)
{
double
mean_prev
=
v
[
0
];
double
stdev_accum
=
0.0
;
double
mean_next
=
0.0
;
for
(
int
i
=
1
;
i
<
size
;
++
i
)
{
mean_next
=
mean_prev
+
(
v
[
i
]
-
mean_prev
)
/
(
i
+
1
);
stdev_accum
+=
(
v
[
i
]
-
mean_prev
)
*
(
v
[
i
]
-
mean_next
);
mean_prev
=
mean_next
;
}
mean
=
mean_next
;
stdev
=
std
::
sqrt
(
stdev_accum
/
(
size
-
1
));
}
int
main
(
int
argc
,
char
*
argv
[])
{
if
(
argc
==
1
)
{
std
::
cout
<<
"Please input a series of floating point numbers:
\n
"
<<
" ./ch-05-ex-04-solution 5.0 4.8 5.3 2.9"
<<
std
::
endl
;
return
-
1
;
}
const
int
n
=
argc
-
1
;
double
*
const
v
=
new
double
[
n
];
for
(
int
i
=
0
;
i
<
n
;
++
i
)
{
v
[
i
]
=
std
::
atof
(
argv
[
i
+
1
]);
}
double
mean
;
double
std_deviation
;
mean_and_std
(
v
,
n
,
mean
,
std_deviation
);
std
::
cout
<<
"The mean and standard deviation are: "
<<
mean
<<
" and "
<<
std_deviation
<<
std
::
endl
;
mean_and_std_rec
(
v
,
n
,
mean
,
std_deviation
);
std
::
cout
<<
"The mean and standard deviation are: "
<<
mean
<<
" and "
<<
std_deviation
<<
std
::
endl
;
delete
[]
v
;
return
0
;
}
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