# displayFormula

Display symbolic formula from string

## Syntax

``displayFormula(symstr)``
``displayFormula(symstr,old,new)``

## Description

example

````displayFormula(symstr)` displays the symbolic formula from the string `symstr` without evaluating the operations. All workspace variables that are specified in `symstr` are replaced by their values.```

example

````displayFormula(symstr,old,new)` replaces only the expression or variable `old` with `new`. Expressions or variables other than `old` are not replaced by their values.```

## Examples

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Create a 3-by-3 matrix. Multiply the matrix by the scalar coefficient `K^2`.

```syms K A A = [-1, 0, 1; 1, 2, 0; 1, 1, 0]; B = K^2*A```
```B =  $\left(\begin{array}{ccc}-{K}^{2}& 0& {K}^{2}\\ {K}^{2}& 2 {K}^{2}& 0\\ {K}^{2}& {K}^{2}& 0\end{array}\right)$```

The result automatically shows the multiplication being carried out element-wise.

Show the multiplication formula without evaluating the operations by using `displayFormula`. Input the formula as a string. The variable `A` in the string is replaced by its values.

`displayFormula("F = K^2*A")`
`$F={K}^{2} \left(\begin{array}{ccc}-1& 0& 1\\ 1& 2& 0\\ 1& 1& 0\end{array}\right)$`

Define a string that describes a differential equation.

`S = "m*diff(y,t,t) == m*g-k*y";`

Create a string array that combines the differential equation and additional text. Display the formula along with the text.

```symstr = ["'The equation of motion is'"; S;"'where k is the elastic coefficient.'"]; displayFormula(symstr)```

Create a string `S` representing a symbolic expression.

`S = "exp(2*pi*i)";`

Create another string `symstr` that contains `S`.

`symstr = "1 + S + S^2 + cos(S)"`
```symstr = "1 + S + S^2 + cos(S)" ```

Display `symstr` as a formula without evaluating the operations by using `displayFormula`. `S` in `symstr` is replaced by its value.

`displayFormula(symstr)`
`$1+{\mathrm{e}}^{2 \pi \mathrm{i}}+{\left({\mathrm{e}}^{2 \pi \mathrm{i}}\right)}^{2}+\mathrm{cos}\left({\mathrm{e}}^{2 \pi \mathrm{i}}\right)$`

To evaluate the strings `S` and `symstr` as symbolic expressions, use `str2sym`.

`S = str2sym(S)`
`S = $1$`
`expr = str2sym(symstr)`
`expr = $S+\mathrm{cos}\left(S\right)+{S}^{2}+1$`

Substitute the variable `S` with its value by using `subs`. Evaluate the result in double precision using `double`.

`double(subs(expr))`
```ans = 3.5403 ```

Define a string that represents a quadratic formula with the coefficients `a`, `b`, and `c`.

```syms a b c k symstr = "a*x^2 + b*x + c";```

Display the quadratic formula, replacing `a` with `k`.

`displayFormula(symstr,a,k)`
`$k {x}^{2}+b x+c$`

Display the quadratic formula again, replacing `a`, `b`, and `c` with `2`, `3`, and `-1`, respectively.

`displayFormula(symstr,[a b c],[2 3 -1])`
`$2 {x}^{2}+3 x-1$`

To solve the quadratic equation, convert the string into a symbolic expression using `str2sym`. Use `solve` to find the zeros of the quadratic equation.

```f = str2sym(symstr); sol = solve(f)```
```sol =  $\left(\begin{array}{c}-\frac{b+\sqrt{{b}^{2}-4 a c}}{2 a}\\ -\frac{b-\sqrt{{b}^{2}-4 a c}}{2 a}\end{array}\right)$```

Use `subs` to replace `a`, `b`, and `c` in the solution with `2`, `3`, and `-1`, respectively.

`solValues = subs(sol,[a b c],[2 3 -1])`
```solValues =  $\left(\begin{array}{c}-\frac{\sqrt{17}}{4}-\frac{3}{4}\\ \frac{\sqrt{17}}{4}-\frac{3}{4}\end{array}\right)$```

## Input Arguments

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String representing a symbolic formula, specified as a character vector, string scalar, cell array of character vectors, or string array.

You can also combine a string that represents a symbolic formula with regular text (enclosed in single quotation marks) as a string array. For an example, see Display Differential Equation.

Expression or variable to be replaced, specified as a character vector, string scalar, cell array of character vectors, string array, symbolic variable, function, expression, or array.

New value, specified as a number, character vector, string scalar, cell array of character vectors, string array, symbolic number, variable, expression, or array.