# Vector Arctangent

## Function Prototype

/* Vector Arctangent */
/* Type: simple */
/* Input arrays: 1    Options: 0    Output arrays: 1 */
/* Inputs: real */
/* Options: none */
/* Outputs: atan */
int ti_atan_start(TI_REAL const *options);
int ti_atan(int size,
TI_REAL const *const *inputs,
TI_REAL const *options,
TI_REAL *const *outputs);

## Description

This documentation is still a work in progress. It has omissions, and it probably has errors too. If you see any issues, or have any general feedback, please get in touch.

Vector Arctangent calculates the Trigonometric arctangent of each element in the input array.

$$atan_{t} = \arctan{input_{t}}$$

This is sometimes useful as a building block to more complex functions.

## Example Usage

### Calling From C

/* Example usage of Vector Arctangent */
/* Assuming that 'input' is a pre-loaded array of size 'in_size'. */
TI_REAL *inputs[] = {input};
TI_REAL options[] = {}; /* No options */
TI_REAL *outputs[1]; /* atan */

/* Determine how large the output size is for our options. */
const int out_size = in_size - ti_atan_start(options);

/* Allocate memory for output. */
outputs[0] = malloc(sizeof(TI_REAL) * out_size); assert(outputs[0] != 0); /* atan */

/* Run the actual calculation. */
const int ret = ti_atan(in_size, inputs, options, outputs);
assert(ret == TI_OKAY);


### Calling From Lua (with Tulip Chart bindings)

-- Example usage of Vector Arctangent
atan = ti.atan(input)


## Example Calculation

dateinputatan
2005-11-010.200.20
2005-11-020.300.29
2005-11-030.400.38
2005-11-040.300.29
2005-11-070.500.46
2005-11-080.700.61
2005-11-090.750.64
2005-11-100.900.73
2005-11-110.900.73
2005-11-141.000.79
2005-11-151.000.79
2005-11-160.200.20
2005-11-170.100.10
2005-11-18-0.10-0.10
2005-11-21-0.50-0.46

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