# Math ¶

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This page list functions that you may use when doing some math. Each course using R will give you more functions/explanations.

## General functions ¶

• summary(x) (mean, min, ...)
• mean(x)
• median(x)
• var(x) (variance)
• cov(x) (covariance)
• cor(x) (correlation)

And you may use

• runif(n): n random values between 0 and 1
• choose(n,k): $C^k_n$ (picking $k$ elements among $n$)
• factorial(n): $n!$
• min(v), max(v)

## Dealing with vectors ¶

• seq(from = x, to = y, length = n)

Create $n$ values inside $[x,y]$. It's something like $step=\frac{y-x}{n-1}$ then you got

$\sum_{i=0}^{n-1} x + step*i$
• rep(v, n): repeat $v$ (vector) $n$ times
• sample(v, n): extract $n$ elements from $v$
• sample(v, n, replace = T): with replacement
• subset(d, cond, var): extract elements for which condition is true
• for instance if we have d\$var, and we want d\$var > 10
• subset(d, var > 10, var)
• cut(x, breaks = v,include.lowest = TRUE)

Cut a vector in intervals. Like $v=c(1,3,5)$ will be $[min,1] \cup ]1,3] \cup ]3,5]$.

## Unused ¶

• circular (cercle trigonométrique)
• outer (Truth table)
• iqr (interquartile range)
• Re, Mod, Img, Arg, Conj
• crossprod: scalar product
• iconv: deal with accents
• Sys.Date, Sys.Timezone, format, weekdays, months, difftime
• dist: distance
• polyroot: roots of a polynomial equation
• uniroot: $f(x) = 0$
• integrate(f, lower = 0, upper = 1)
• taylor (package pracma)