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cordiccart2pol

Transform Cartesian coordinates to polar using CORDIC-based approximation

Syntax

``[theta,rho] = cordiccart2pol(x,y)``
``[theta,rho] = cordiccart2pol(x,y,niters)``
``[theta,rho] = cordiccart2pol(___,'ScaleOutput',b)``

Description

example

````[theta,rho] = cordiccart2pol(x,y)` transforms corresponding elements of data stored in Cartesian coordinates `x` and `y` to polar coordinates `theta` and `rho` using a CORDIC algorithm approximation.```
````[theta,rho] = cordiccart2pol(x,y,niters)` performs `niters` iterations of the CORDIC algorithm.```
````[theta,rho] = cordiccart2pol(___,'ScaleOutput',b)` specifies whether to scale the output `rho` by the inverse CORDIC gain value.```

Examples

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Convert fixed-point and floating-point Cartesian coordinates to polar coordinates using a CORDIC algorithm approximation. Compare the results to the MATLAB® `cart2pol` function.

```[theta_c2p_flt,rho_c2p_flt] = cordiccart2pol(-0.5,0.5) [theta_c2p_fxp,rho_c2p_fxp] = cordiccart2pol(fi(-0.5,1,16,15),fi(0.5,1,16,15)) [theta_mlb_flt,rho_mlb_flt] = cart2pol(-0.5,0.5)```
```theta_c2p_flt = 2.3562 rho_c2p_flt = 0.7071 theta_c2p_fxp = 2.3562 DataTypeMode: Fixed-point: binary point scaling Signedness: Signed WordLength: 16 FractionLength: 13 rho_c2p_fxp = 0.7071 DataTypeMode: Fixed-point: binary point scaling Signedness: Signed WordLength: 18 FractionLength: 15 theta_mlb_flt = 2.3562 rho_mlb_flt = 0.7071```

Convert an array of fixed-point Cartesian coordinates to polar coordinates using a CORDIC algorithm approximation.

```[theta_pos,rho] = cordiccart2pol(fi([0.75:-0.25:-1.0],1,16,15),fi(0.5,1,16,15)) [theta_neg,rho] = cordiccart2pol(fi([0.75:-0.25:-1.0],1,16,15),fi(-0.5,1,16,15))```
```theta_pos = 0.5881 0.7854 1.1072 1.5708 2.0344 2.3562 2.5535 2.6780 DataTypeMode: Fixed-point: binary point scaling Signedness: Signed WordLength: 16 FractionLength: 13 rho = 0.9014 0.7071 0.5591 0.5000 0.5591 0.7071 0.9014 1.1180 DataTypeMode: Fixed-point: binary point scaling Signedness: Signed WordLength: 18 FractionLength: 15 theta_neg = -0.5881 -0.7854 -1.1072 -1.5708 -2.0344 -2.3562 -2.5535 -2.6780 DataTypeMode: Fixed-point: binary point scaling Signedness: Signed WordLength: 16 FractionLength: 13 rho = 0.9014 0.7071 0.5591 0.5000 0.5591 0.7071 0.9014 1.1180 DataTypeMode: Fixed-point: binary point scaling Signedness: Signed WordLength: 18 FractionLength: 15```

Input Arguments

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Cartesian coordinates, specified as scalars, vectors, matrices, or multidimensional arrays. `x` and `y` must be the same size. If they are not the same size, at least one value must be a scalar. Both `x` and `y` must have the same data type.

Data Types: `single` | `double` | `int8` | `int16` | `int32` | `int64` | `uint8` | `uint16` | `uint32` | `uint64` | `fi`

Number of iterations the CORDIC algorithm performs, specified as a positive integer-valued scalar. Increasing the number of iterations can produce more accurate results but also increases the expense of the computation and adds latency.

If you do not specify `niters`, or if you specify a value that is too large, the algorithm uses a maximum value based on the data type of the inputs:

• Fixed-point inputs — The maximum number of iterations is the word length of `rho` or one less than the word length of `theta`, whichever is smaller.

• Floating-point inputs — The maximum value is `52` for `double` or `23` for `single`.

Data Types: `single` | `double` | `int8` | `int16` | `int32` | `int64` | `uint8` | `uint16` | `uint32` | `uint64` | `fi`

Whether to scale the output `rho` by the inverse CORDIC gain value, specified as one of these values:

• `1` — Multiply output values by a constant. This incurs extra computations.

• `0` — Do not scale the output.

Data Types: `single` | `double` | `int8` | `int16` | `int32` | `int64` | `uint8` | `uint16` | `uint32` | `uint64` | `logical` | `fi`

Output Arguments

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Angular coordinate, returned as an array. `theta` is the counterclockwise angle in the x-y plane measured in radians from the positive x-axis. The value of the angle is in the range `[-pi pi]`.

If `x` and `y` are floating-point, then `theta` has the same data type as `x` and `y`. Otherwise, `theta` has a fixed-point data type with the same word length as `x` and `y` with a best-precision fraction length for the `[-pi pi]` range.

Radial coordinate, returned as an array. `rho` is the distance from the origin to a point in the x-y plane.

`rho` returns the polar coordinates radius magnitude values. `rho` is real-valued and can be a scalar or have the same dimensions as `theta`.

If the inputs `x,y` are fixed-point values, then `rho` is a signed fixed-point value with binary-point scaling. If the inputs `x,y` are signed, then the word length of `rho` is the input word length `+2`. If the inputs are unsigned, then the word length of `rho` is the input word length `+3`. The fraction length of `rho` is always the same as the fraction length of the `x,y` inputs.

More About

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CORDIC

CORDIC is an acronym for COordinate Rotation DIgital Computer. The Givens rotation-based CORDIC algorithm is one of the most hardware-efficient algorithms available because it requires only iterative shift-add operations (see References). The CORDIC algorithm eliminates the need for explicit multipliers. Using CORDIC, you can calculate various functions such as sine, cosine, arc sine, arc cosine, arc tangent, and vector magnitude. You can also use this algorithm for divide, square root, hyperbolic, and logarithmic functions.

Increasing the number of CORDIC iterations can produce more accurate results, but doing so increases the expense of the computation and adds latency.

Algorithms

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Signal Flow Diagrams

CORDIC Vectoring Kernel

The accuracy of the CORDIC kernel depends on the choice of initial values for X, Y, and Z. This algorithm uses the following initial values:

fimath Propagation Rules

CORDIC functions discard any local `fimath` attached to the input.

The CORDIC functions use their own internal `fimath` when performing calculations:

• `OverflowAction``Wrap`

• `RoundingMethod``Floor`

The output has no attached `fimath`.

Version History

Introduced in R2011b